This article summarizes the origins of CDMA technology and the introduction of 3G versions such as CDMA2000 1X and CDMA2000 1x EV-DO. An overview of the network architecture is presented with detailed explanations of the role of each component and interface in the network and protocol testing to change the needs of the network. The article ends with a discussion of some of the technical issues that may arise in CDMA networks and some suggested solutions.
Code Division Multiple Access (CDMA) technology has emerged as an alternative to GSM cellular architecture and has contributed to explosive growth in the wireless market over the past decade. CDMA, like GSM, has made continuous improvements throughout this period. Both networks are in the process of transitioning to 3G systems globally, allowing more capacity and data services.
Digital revolution and development situation
While the mobile communications industry started with the transition from first generation analogue to second generation digital architecture, in Europe, the GSM architecture became popular, while in the US America, parts of Asia & nbsp; Asia and elsewhere, CDMA "spread-spectrum" technology has occupied a large market share. Because of the "spread spectrum" using broadband, interference signals are often difficult to detect. They are not easily blocked or demodulated. In addition, "spread spectrum" signals are often more difficult to jam (jam) than narrow band signals. The LPI (Low Probability of Intercept) and AJ (antijam) characteristics are the main reasons why the military has used the "spread spectrum" for many years. Both GSM and CDMA network technologies are improving in terms of bandwidth, adding features and reliability at lower cost to retain customers.
CdmaOne supports 2G mobile communication to forget
The TIA / EIA CDMA IS-95 (published in July 1993) establishes the fundamentals for end-to-end wireless communications. The commercial network architecture based on this standard is known as CdmaOne. The TIA / EIA IS-95 and subsequent IS-95A (released in March 1995) provide the basis for most CDMA 2G-based networks deployed around the world.
From the perspective of voice services, CdmaOne technology provides important features for mobile operators such as:
The increase in voice capacity from 8X to 10X shows a better performance compared to analog AMPS systems.
Simplified network planning, with the same frequency used in each region of each cell.
The CDMA 2G infrastructure was originally shown to be efficient in delivering high-quality, low-loss voice traffic. However, it does not last long as mobile users start demanding basic data services such as Internet and Intranet services, multimedia applications or fast-paced commercial transactions. Height is added to voice services on their phones. The TIA / EIA IS-95A fulfills this requirement by defining a 1.25 MHz CDMA broadband channel, power control, call handling, hand-off techniques and registration. registration) for the operation of the system. IS-95A TIA / EIA has provided the appropriate channel-switching data services for CDMA subscribers. However, these services are limited to a maximum speed of 14.4 Kbit / s per user.
The second edition of the revised version of the original specification has produced the IS-95B TIA / EIA standard. This standard provides subscribers with packet-switched data services at rates up to 64 Kbit / s per subscriber in addition to existing voice services. With increased data rates, IS-95B TIA / EIA compatible networks are considered as 2.5G CDMA technology.
Cdma2000 replaces CdmaOne
The transition to 3G is still being implemented with a large number of new standards being proposed. Some are based on GSM infrastructure and others come directly from CDMA. In the end, the ITU also defined an IMT-2000 standard consisting of five different radio interfaces, including CDMA2000. Note that all IMT-2000 protocols use "spread-spectrum" [5] technology in connection with network installation, operation, and maintenance.
ITU defines a 3G network as a communications network in which system capacity and spectrum efficiency are improved compared to 2G systems. 3G supports data services with a minimum transfer rate of 144 kbit / s in a mobile environment and 2 Mbps in a fixed environment. The CDMA2000 architecture faces the above goals and includes some additions that an operator can choose to serve as a transition strategy based on existing infrastructure, pricing, and some other factors.
These additions include CDMA2000 1X and CDMA2000 1xEV:
+ CDMA2000 1X doubles the voice capacity of CdmaOne networks, allocating maximum data rates of 307 Kbit / s to each subscriber in a mobile environment.
+ CDMA2000 1xEV consists of two variants, both backwards compatible with CDMA2000 1X and CDMAOne technologies.
CDMA2000 1xEV-DO (Data Only) is capable of delivering multimedia data services such as MP3 streaming, video conferencing with a maximum data rate of 2.4 Mbit / s per subscriber. mobile environment.
CDMA2000 1xEV-DV (Data Voice and Voice) provides simultaneous voice and data services with simultaneous data rates up to 3.09 Mbps for subscribers.
A network structure designed for packet-switched communications
Figure 1 illustrates a simplified CDMA2000 1X network, showing both the telephone structure (ANSI-41, see end of article) and data. Refer to Figure 1 for further discussion.
Figure 1: Structure of a CDMA network . (Note all the symbols and concepts on the drawing are explained in the acronym or footnote & nbsp; in part 2 of the article).
Mobile Station (MS - Mobile Station)
In a CDMA2000 1X network, the mobile station MS - which is the subscriber of a CDMA cellular or mobile network - acts as a mobile IP client.
The mobile station interacts with the Access Network to obtain the appropriate wireless resources for exchanging packets and monitoring the status of radio resources including "active", "stand" -by "(backup)," dormant "(inactive). It accepts packets from a mobile host when radio resources are not available or sufficient to support traffic on the network.
Thanks to the power supply, the mobile station automatically registers with the HLR (Home Location Register) to:
Authentication of mobile devices is in the environment of the access network. Gives HLR the current location of the mobile device. Provides the Mobile Terminal Services (MSC-S) feature set for mobile devices.
After successful registration with the HLR, the mobile device is ready to make voice and data calls. These calls can be in the form of circuit-switched data (PSD) or PSD (packet-switched data), depending on the compatibility of the mobile device itself. (or incompatible) with the IS-2000 standard. This document defines protocols for various CDMA interfaces related to the transmission of packets named A1, A7, A9 and A11.
Mobile MS stations must comply with IS-2000 standards to initiate a packet data session using the 1xRTT1 network [4]. Mobile stations only have IS-95 capabilities limited by CSD, while optional IS-2000 terminals are either PSD or CSD. The terminal-by-link parameter (AL-air link) to the network determines the type of service required.
Channel-switching data has a maximum speed of 19.2 Kbit / s and is implemented through traditional TDM channels. This service allows the user to select a point of attachment in a data network using regular dialing.
The packet data service has a maximum data rate of 144 Kbps. For each data session, a PPP (Point-to-Point Protocol) session is created between the mobile station and the PDSN (Packet Data Serving Node). Assigning an IP address to each mobile device can be provided by the PDSN or a Dynamic Host Configuration Protocol (DHCP) server via a Home Agent (HA).
(Wireless access network)
RAN (Radio Access Network) is the entry point of a mobile subscriber for data or voice communications including:
Air link Cell tower and antenna and cable connection to BTS (Base Station Transceiver Subsystem) BTS to BSC (Abis) BSC (Base Station Controller) ) PCF (Packet Control Function)
In particular, RAN has a number of responsibilities that affect the provision of packet network services. RAN must map to the mobile client identity referencing a unique link layer identity used to communicate with the PDSN, validate the mobile station for the access service, and maintain transmission links. established.
(Base Station Transceiver Subsystem) controls the operation of air link and has the interface between the network and the mobile device. RF resources such as frequency assignment, regional allocation, and source control are managed by the BTS. In addition, the BTS manages the traffic from the location of the coverage area to the Base Station Controller (BSC) to minimize any delay between these two components. Usually, a BTS connects to the BSC via un-channelized T1 or directly to the cable in the same location. The protocols used within this medium are exclusively based on the High-level Data Link Control (HDLC) platform.
The Base Station Controller routes voice messages and circuit-switched data between the cell site and MSC. It also has a role of mobility management that controls and governs "hand-off" from one cell site to another where it is needed. The BSC connects to each MTX that uses T1 channels for channel and channel switching and to non-channel T1 lines for signaling and control messages to the PDSN using the 10BaseT Ethernet protocol.
The Packet Control Function routes packet data between the mobile station within the cell and PDSN (Packet Data Serving Node) locations. During the packet data sessions, the PCF will allocate available sub channels as needed to comply with the services required from mobile and prepaid subscribers. The PCF maintains a "reachable" state between the RN and the mobile station to ensure a persistent link for packets, buffering packets coming from the PDSN while radio resources are not available or sufficient. Supports traffic from PDSN and forwards packets between MS and PDSN.
The core network role in CDMA infrastructure
Packet Data Serving Node / Foreign Agent (PDSN / FA)
PDSN / FA is the gateway from the RAN to the public or private packet networks. In a simple IP network, the PDSN acts as a stand-alone NSA (Network Access Server), whereas in a mobile IP network it can be configured as a Home Agent (HA) or a FA (Foreign Agent).
The PDSN performs the following functions:
Management of radio packet interfaces between the Base Station Subsystem (BSS) and the IP network by establishing, maintaining, and connecting the link layer to the mobile client.
• End PPP session created by the subscriber.
• Provide an IP address to the subscriber.
Perform packet routing to external packet data networks or packet routing to optional HAs to become secure tunnels.
• Collect and forward data packets.
• Manage subscriber services based on the profile obtained from the SCS server of the AAA server [1].
• Authenticate local users or forward authentication requests to AAA servers.
(End of Part I)
