[Part 1 begins with a look at interworking objectives and requirements, as well as interworking schemes to connect WLANs and 3G networks. Part 2 examines the tight coupling interworking approach, where the WLAN is connected to the 3GPP (GPRS) core network in the same way as any other radio access network. Part 3 covers loose coupling, where the WLAN data traffic doesn't pass through the GPRS core network but goes directly to the operator's IP network.]
22.9 Local Multipoint Distribution Service
Local multipoint distribution service (LMDS) with two-way capability gives long-distance carriers a relatively cheap entree into the local market with multiple operating benefits.
LMDS is a new type of stationary broadband wireless access technology designed for a mass subscriber marketplace (see Figure 22.18). It is based on millimeter micro frequencies - 2.4 GHz and above. LMDS now offers a potential for cheaper in-building bandwidth than fiber or copper.
Figure 22.18 Example of LMDS configuration.
in LMDS denotes that propagation characteristics of signals in this frequency range limit potential coverage area of a single cell site; ongoing fi eld trials conducted in metropolitan centers place the range of an LMDS transmitter up to 5 miles.
Multipoint indicates that signals are transmitted in the point-to-multipoint or broadcast method; the wireless return path, from the subscriber to the base station, is a point-to-point transmission.
Distribution refers to the distribution of signals, which may consist of simultaneous voice, data, Internet, and video traffi c.
Service implies the subscriber nature of the relationship between the operator and customer; the services offered through an LMDS network are entirely dependent on the operator's choice of business.
LMDS is an ideal candidate for integrating voice and data in new multitenant buildings. With just an antenna at the end-user site, located within 3 to 5 km of an operator's two-way LMDS cell, the access technology can deliver large bandwidths. Corporate applications can include anything from Ethernet and fast Ethernet LAN extension to full-scale campus networking, alternative cable TV, video-conferencing, high-speed Internet access, and corporate video on demand.
LMDS transmissions are strictly line-of-sight. For this reason, carriers are apt to target business districts where rooftop mounting of subscriber dishes is permissible. LMDS services are permitted at a number of frequencies: 24 GHz, 28 GHz, 31 GHz, 38 GHz, and soon 40 GHz. The 28 GHz region has a spectrum allocation of 1.3 GHz, and currently offers the greatest potential for bundling diverse services. The capacity of 28 GHz LMDS, consisting of three bands - 27.5 to 28.35 GHz, 29.10 to 29.25 GHz, and 31.0 to 31.5 GHz - is such that the system can accommodate high-speed Internet access.
Other applications of LMDS include multiple virtual private networks for corporations and government agencies or ATM telephony and streaming video, including video broadcasting. LMDS is seen primarily as a data pipe. LMDS operators have plans for supporting all kinds of corporate network services, including secure file transfer and messaging within a virtual LAN context, video conferencing, and IP telephony. In LMDS, a data access scheme can be FDMA, TDMA, or CDMA. The typical data rate of LMDS is 45 Mbps.
Advantages of LMDS for broadband are:
- Lower entry/deployment costs than wireline
- Ease/speed of deployment
- Fast realization of revenue (resulting from rapid deployment)
- Scalable architecture (demand-based build-out)
- No stranded capital when customers leave
- Cost-effective network maintenance, management, and operations
The IEEE 802.16.2 standard focuses on the coexistence of a fixed broadband wireless access (BWA) system with other wireless systems and provides recommendations for the design and coordinated deployment of fixed broadband wireless access systems in order to control interference and facilitate coexistence. IEEE 802.16.2 analyzes appropriate coexistence scenarios and provides guidance for system design deployment, coordination, and frequency usage. IEEE 802.16.2 covers 2 to 66 GHz frequencies, with a detailed emphasis on 3.5, 10.5, and 23.5 to 43.5 GHz frequencies.
The following are the present IEEE 802.16 standards:
- P802.16a: 2–11 GHz licensed band; addresses point-to-multipoint BWA systems, OFDM, and single-carrier systems
- P802.16b: license-exempt bands, with focus on 5–6 GHz; wireless high-speed unlicensed metropolitan area network (HUMAN), OFDM
- P802.16.2: focuses on 2–11 GHz frequency band and the coexistence of BWA systems