Transitions to 3G for Wireless WANs (WWANs)

Without losing sight of the fact that hotspot services rely mostly on WLANs and WPANs, we close the technical part of this book by summarizing the anticipated evolution from the current-base WWAN system to the target system over the next three to five years. This evolution is expected to be as follows:

  • Hotspot: IEEE 802.11b to IEEE 802.11a or IEEE 802.11b to IEEE 802.11g

  • CDMAOne IS 95A (to cdmaOne IS-95B) to CDMA2000 1x to CDMA2000 1x EV-DO or EV-DV

  • TDMA to CDMA2000 1x . . . or

  • TDMA to GSM . . .

  • GSM to GPRS to EDGE to W-CDMA

As just remarked, W-CDMA is the 3G technology called for in UMTS. W-CDMA is part of the ITU IMT-2000 standard. Thanks to the efficient use of the radio spectrum, a wealth of different services can be accessed simultaneously, including circuit and packet services. Data speeds can be as high as 2 Mbps. W-CDMA data speeds are expected to go up to 10.8 Mbps in 3GPP Release 5. W-CDMA is also the recommended upgrade path for GSM operators. Forecasters make the claim that with the upgrade to W-CDMA, GSM will likely hold an 80 percent market share in 2005.

Work is also under way to interwork 2.5G/3G WWANs with WLANs. Figure 9-7 suggests three scenarios. In the first, the WWAN network handles mobility, specifically GPRS. Here the WLAN is considered as one of the GPRS cells. This approach may require dual-mode network interface cards (NICs) to access the two different Layer 2 services. All traffic reaches the Serving GPRS Support Node (SGSN) or Gateway GPRS Support Node (GGSN) before reaching its intended final destination (this happens even if the final destination is the WLAN or LAN itself). In the second scenario, mobility is handled by the WLAN based on IEEE 802.11 rules. In the third scenario, a mobility gateway handles mobility. It also handles routing issues using Mobile IP (see Chapter 3) to handle mobility management. The mobility gateway is located between the GPRS and the WLAN networks. The gateway is a proxy that can be implemented in either the GPRS or the WLAN (both of these networks being considered peers).

click to expand
Figure 9-7: 2.5G/3G-to-WLAN interworking

As we covered in the text, IEEE 802.11a (also known as Wi-Fi 5) supports 54 Mbps in the 5 GHz band. There are already products on the market (both access points and PC/desktop NICs) from companies such as Proxim, Intel, D-Link, and Actiontec. However, it is a well-know fact that it is easier to reach longer distances at a lower transmission speed (also within the context of the IEEE 802.11b speed choices). At this time the consensus is that IEEE 802.11b will continue to be the hotspot technology of choice at least until 2004. Depending on field-strength validations with the IEEE 802.11a technology, this technology may or may not usurp to role for hotspots. In any event, the system bottleneck may well be on the terrestrial uplink into the Internet, so that the speed on the air link is, by itself, of limited value. Only when the uplink is increased to 10 Mbps or DS-3, the air link speed starts to make a difference. It should also be noted that, although the IEEE 802.11a standards was first approved in 1999, the technology has been slow taking off not only because engineering the 802.11a chipsets is proven challenging, but also because the success of 802.11b has made it a de facto standard.

IEEE 802.11g aims at supporting 54 Mbps in the 2.4 GHz band. It is designed to be backward compatible with existing Wi-Fi devices. Products were expected for early 2003. The same observations just made with regards to IEEE 802.11a apply here. Furthermore, while both IEEE 802.11a and 802.11g may be beneficial for indoors WLAN technologies, they likely will have a harder time in open-space hotspot services. This is because higher speeds are more susceptible to noise and interference. Hence, an unprotected open ISM environment may prove problematic for these technologies.



Hotspot Networks(c) Wi-Fi for Public Access Locations
Hotspot Networks(c) Wi-Fi for Public Access Locations
ISBN: N/A
EAN: N/A
Year: 2005
Pages: 88

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