Wimax standards and Security The Wimax

2G


FIGURE 1.4
Evolution of cellular technology.

(ARIB) in Japan, the Telecommunication Technology Committee (TTC) in Japan, the Alliance for Telecommunications Industry Solutions (ATIS) in the United States, the China Communications Standards Association (CCSA) in China, the Telecommunications Technology Association (TTA) in Korea, and the European Telecommunications Standards Institute (ETSI). Together, these standards bodies comprise the organizational partners for 3GPP. The 3GPP project agreement signed by all the organizational partners states that they shall cooperate in producing “globally applicable’’ technical specifi- cations and reports for a 3G mobile system based primarily on GSM core networks and the radio access technologies they support, such as enhanced data rates for GSM evolution (EDGE), high-speed data packet access, or uni- versal terrestrial radio access (UTRA). The 3GPP was established primarily for preparation, approval, and maintenance of technical specifications and reports for 3G networks based on the GSM core structure. Furthermore, 3GPP is not considered a legal entity.

The 3GPP2 was established in December 1998 as a collaboration between
multiple regional telecommunications standards bodies: the ARIB in Japan, the CCSA in China, the Telecommunications Industry Association (TIA) in North America, the TTA in Korea, and the TTC in Japan. Together, these stan- dards bodies comprise the organizational partners for 3GPP2. Also, market representation partners include the CDMA Development Group, the IPv6 Forum, and the International 450 Association. These market representation partners offer market advice and a consensus view on market requirements. The 3GPP2 was established primarily for preparation, approval, and main- tenance of technical specifications and reports for 3G networks based on the cdma2000 core network structure. Like 3GPP, 3GPP2 is not considered a legal entity.
The 3G cellular standards addressed by the 3GPP and 3GPP2 can be placed in one of the two respective categories: TDMA or CDMA. TDMA technology operates on the premise that a user on the network has a time slot allocated on the cellular channel. Here, a user occupies the entire bandwidth of that channel for a specified periodic time frame with some period T. Within the length of the period T, many users can occupy the entire bandwidth, as long as each one’s time frame does not overlap with the other. As a consequence, accurate, precise timing in a TDMA system from the BS and user perspective is critical. Generally, the bandwidth of each channel is around 200 kHz for GSM-TDMA systems employed today. Furthermore, each channel can hold approximately five to six users at one time. Once all time slots are filled, the TDMA channel is considered to be at full capacity, and no more users can be accommodated until one of the current users disconnects from the system. The advantage of TDMA is that the sound quality is consistent as long as a time slot is available to serve a mobile user. However, once all time slots are filled with mobile users, service is denied to all the other users.
CDMA technology operates quite differently from TDMA. Each user data
channel is multiplied by a unique, mathematically orthogonal binary chip- ping sequence at a much faster rate than the symbol rate of the modulation


used. This, in effect, spreads the spectrum of each user to cover a bandwidth of about 1 MHz, so all users share the entire spectrum at the same time and with the same power. Interference is minimized in this approach for two rea- sons. First, each unique chipping sequence is orthogonal to the next one in signal space. These chipping sequences are called Walsh codes. There are 64 unique Walsh codes. Second, a high-fidelity, rapidly adapting power con- trol mechanism employed at the BS’ and mobile users maintain near-equal received power levels from mobile users, as seen by the BS, so no one user has a power advantage over another. Open- and closed-loop power control methods are employed here. The open-loop power control method employs BS observations of power measurements from mobile users. The BS may com- mand a mobile user to adjust its power to match the received signal levels of the other mobile users. The open-loop method operates at a relatively slow rate as compared to closed-loop power control in which the mobile user is an active part of the power control and adjusts its own power based on its observations of received power levels from the BS. CDMA has an advantage over TDMA when considering capacity degradation. While TDMA hard lim- its the number of users who may use the channel at one time, CDMAallows for a more gradual degradation in quality for each additional user. All active users suffer slight quality degradation when another user joins the network at the same time. However, this can result in a significant variation in sound quality, as compared to the relative consistency of the time slot method employed in TDMA.
While the second generation of both these technologies supported data
rates up to 14.4 Kbps (CDMA) and 9.6 Kbps (TDMA), these speeds would not provide the necessary bandwidth to support the applications used on today’s wireless Internet architecture. However, evolution to third-generation technology data rates (around a megabit per second) has improved the performance of these high-bandwidth applications.
Today, users have an option with most cellular companies to purchase a Personal Computer Memory Card International Association (PCMCIA) net- work access card to connect to the Internet. Typical data rates experienced by users range from 300 Kbps up to 1 Mbps, depending on the technology. To date, evolved CDMA technologies such as 1xEVDO have outperformed evolved GSM technologies such as the Universal Mobile Telecommunications System-Wideband CDMA (UMTS-WCDMA) from a data rate perspective. 1xEVDO currently supports a downlink physical layer data rate at 2.4 Mbps and an uplink physical layer data rate at 150 Kbps. Revision A to this stan- dard will improve the downlink physical layer data rate to 3.1 Mbps and increase the uplink physical layer data rate to 1.8 Mbps. The high-speed down- link packet access (HSDPA) standard for UMTS-WCDMA aims to support downlink physical layer data rates from 1.8 up to 7.2 Mbps and beyond by introducing another channel known as the high-speed downlink shared chan- nel (HSDSCH) used solely for downlink communications to the mobile user. The uplink data rate supported by HSDPA is 384 Kbps. More information on these standards and their evolution is discussed in Ref. 5.

Cellular network providers have adopted strategies to evolve their net- works to third generation, and most have currently adopted the new technologies available. However, cellular networks are most useful for pro- viding their first envisioned application: voice. Nevertheless, these network providers have noticed the evolving wireless Internet architecture unfold, especially with the success of IEEE 802.11, and as such desire to participate by providing increased data rates and services to compel users seeking wire- less network access to utilize the cellular infrastructure. While coverage for cellular networks is by far the most extensive of any wireless network infra- structure deployed to date (with the exception of low-bandwidth satellite), data rates have yet to evolve to support the increasing bandwidth needs of users.

3.