 |
|
|
The world is going to 3G at a rapid rate, but who has the map? Massive technology juggernauts, both carriers and manufacturers, are realigning, trying to decide which direction (or directions) they want to explore. Even the terminology being used is radically different, making it difficult for people to even determine which way is up on the new map!
The world appears to have agreed that the long term future for wireless communications is with CDMA, but TDMA carriers believe that their technology is far from played out. The pure CDMA initiative has its own standards committee in 3GPP2 (Third Generation Partnership Project 2, www.3gpp2.org) and the “TDMA now, CDMA tomorrow” initiative is working with the confusingly similarly named 3GPP (Third Generation Partnership Project, www.3gpp.org).
The wonderful world of wireless has had periods of explosive innovation and periods of consolidation in its two hotbeds of development – Europe and North America. In the early days of analog, there were numerous protocols in Europe, while North America had the single AMPS standard (apart from the Aurora-400 system in Alberta). Europe realized that it was divided, and to avoid being conquered, joined hands to design the first major digital cellular system – GSM. This immediately put North America on the defensive. Their reaction was D-AMPS, which was planned to allow TDMA to gradually supplant analog, by filling one 30 kHz analog channel with 3 digital timeslots. However, harmony was almost immediately broken when the proponents of the upstart CDMA technology started singing a different tune, using 1.25 MHz channels for a single carrier. Whereas once, world domination was clearly within the grasp of the AMPS technology, dominated by North American companies, soon GSM caught up, and then surpassed AMPS, giving European companies the edge. Although D-AMPS (now known as ANSI-136) and CDMA (IS-95 and ANSI-95) have achieved significant penetration, they do not have the single unified market of Europe behind them.
Today brings another period of realignment, with regional barriers finally being broken. The GSM and ANSI-136 choirs are joining to learn to sing together, bringing the major European carriers, as well as North American TDMA powerhouses such as AT&T Wireless, Cingular, VoiceStream, Rogers AT&T and Microcell, together – certainly a formidable force. CDMA has more of a North American/Asian focus, with little likelihood of significant penetration in Europe where everyone sings the same tune – GSM. The ability to present a road map that connects today’s systems with tomorrow’s 3G systems is critical for carriers and vendors alike to retain the confidence of their customers and shareholders, although it is fair to say that both road maps have some uncharted territory to cross. And who knows what swamps this territory may include.
There may still be some people in the ITU ivory towers who believe that their IMT-2000 project will result in a single global standard, however their reluctant acceptance of the ‘family of standards’ concept means that the best that can be hoped for is that the two families will be good neighbors and learn to work together, and that they do not divide any further or start any messy fights.
There are signs that the 3GPP and 3GPP2 families are willing to work together on some major issues, as both have accepted an authentication method, known as AKA. Currently, the methods used in North America (CAVE for analog, ANSI-136 TDMA and ANSI-95 CDMA) are completely different and incompatible with the methods used in GSM. AKA brings a higher level of security, along with important concepts from both GSM authentication and the CAVE-based system. The use of common authentication standards is very important, because without it carriers have a choice of very insecure cross-technology roaming or very expensive cross-technology roaming (due to the need to maintain individual subscriber records wherever protocol interworking is performed).
Although the IMT-2000 goal of a single, universal 3G system might not be achieved, 3GPP and 3GPP2 are both aiming to achieve the performance requirements of this project, largely defined as higher data speeds. These are:
The focus on speed represents a bit of a dilemma because the other major application for wireless (talking) only requires data rates of around 8-13 kbps. And, if carriers could get satisfactory speech quality with lower bit rates (e.g. 4 kbps), they would jump at the chance. So, although vendors can provide virtually any data speed that might be desired, up to the total bit rate of an entire channel, it comes at an increasing price in terms of equivalent voice users. Even at the sub-3G speed of 80 kbps, a data user is taking as much bandwidth as 10 voice users. Will they be charged 10 times as much, or will access to huge quantities of 3G spectrum mean that carriers no longer have to be so concerned about how they parcel out their spectrum?
TDMA standards have been very successful, providing the majority of customers with their first taste of digital cellular. GSM is now the most widely used cellular/PCS standard in the world, and D-AMPS (ANSI-136) is also in widespread use, particularly in North and South America. However, due to the relatively rigid structure of TDMA channels, these systems are less flexible when it comes to providing higher speed data, although they are more flexible in other areas, such as providing wireless office systems.
The proponents of 3GPP standardization first want to bring GSM and D-AMPS closer together through the GPRS and EDGE systems that use more efficient modulation schemes to achieve higher bit rates. This also provides a transition from the 30 kHz wide channels used in D-AMPS (inherited from analog) to the 200 kHz channels used in GSM. Wider channels allow even higher data rates to be used, allowing for basic 3G speeds of 144 kbps to be achieved.
3GPP performs its standardization activities in several Technical Specification Groups (TSGs):
TSG-SA (Services & Architectures) provides the direction for 3GPP, defining features and coordinating the activities of the other TSGs.
TSG-GERAN (GSM-EDGE Radio Access Network) has inherited the standardization of GSM from ETSI. TIA subcommittee TR-45.3 still has responsibility for maintaining the ANSI-136 standard, but has recently rejected a suggestion to become a partner in 3GPP.
TSG-T (Terminals) is responsible for mobile station standards, including the “Smart Card” that is a characteristic of GSM phones, and will be retained in 3G.
TSG-RAN (Radio Access Network) is responsible for 3G radio interfaces, including Wideband CDMA and UTRA, which are planning to achieve speeds of 2 Mbps.
TSG-CN (Core Network) is responsible for network standards that allow for roaming, validation and authentication and other mundane tasks that put the “Access” in a radio protocol. This protocol is expected to inherit a lot from the GSM MAP and a little bit from ANSI-41, as well as new concepts and capabilities.
3GPP is a partnership of major standards organizations from around the world: ETSI from Europe, ATIS T1P1 from North America, CWTS from China, TTA from Korea and ARIB and TTC from Japan.
|
If you believe that CDMA is the only game in town, 3GPP2 is the standards committee for you. Its members claim that TIA/EIA-95 CDMA (aka ANSI-95, cdmaOne) covers the basics of voice and low data speeds, and that it soon will be at the 2.5G level with higher speed data in the cleverly named IS-2000 (aka cdma2000). 3GPP2 hopes to achieve basic 3G data rates of 144 kbps with 1xRTT, and the top 3G rates of 2 Mbps with Qualcomm’s HDR (imaginatively named “High Data Rate”). Future systems that are being discussed (such as the Nokia/Motorola 1XTREME proposal) could achieve top data rates of 5 Mbps, although it is not likely that this would often be given to a single user.
3GPP2 is divided into several TSGs (Technical Specification Groups), as shown in Figure 2.
TSG-S plays a similar role to TSG-SA in 3GPP, that of requirements specification and coordination.
TSG-C is responsible for developing CDMA radio interface standards, and is closely associated with TIA standards committee TR-45.5 that originally developed TIA/EIA-95 and IS-2000 CDMA standards. This somewhat parallels the activities of TSG-RAN and TSG-T in 3GPP.
TSG-N is responsible for network standards, based on the existing TIA/EIA-41 Mobile Application Part that is still being standardized by TIA TR-45.2.
TSG-P is responsible for packet data standards, and is closely associated with TIA subcommittee TR-45.6 that was initiated to bless the CDPD (Cellular Digital Packet Data) protocol, that converted analog channels into digital packet data channels.
TSG-A is responsible for protocols between base stations and MSCs, and works closely with TIA TR-45.4 that developed the “A” interface used by many CDMA carriers.
TSG-R was tasked with achieving interworking with 3GPP, however there appears to be no interest in this at present from either side, and it has no plans to meet within the next year or so.
The partners in 3GPP2 are surprisingly similar to 3GPP. CWTS from China, TTA from Korea and ARIB and TTC from Japan are partners in both organizations. ETSI and ATIS are, however, replaced by the TIA, which plays a leading role because of its sponsorship of all the TIA TR-45 subcommittees which are still developing AMPS, D-AMPS and CDMA standards, as well as the ANSI-41 network standard to support them.
|
The ink is not even dry on 3G standards, and already engineers are frantically working on 4G standards. Here the focus is not so much on the radio interfaces as on a migration to Internet Protocols. Both 3GPP and 3GPP2 are investigating “All IP” systems, where the many fractured protocols of 2G systems (radically different standards for radio interfaces, “A” interfaces, wireless network interfaces and PSTN interfaces) will be replaced by end-to-end IP protocols. While this opens up new possibilities for telecommunications services and seamlessness, it also opens up a wide variety of new problems, such as ensuring security, reliable performance and robustness.
The development of 3G standards represents a major change in direction. Attention is being turned away from voice services to data, and the European/North American divide is being replaced by a TDMA/CDMA divide. We may have to wait until 4G before there is a single universal radio communications system!
© – Copyright