Modulation and Line-Coding Techniques in Hybrid Networks

To prevent confusion, hybrid terminology refers to a combination of wired and wireless technologies. These technologies are available in today's market and offer some unique features. The wireless modem works as an integrated part of the Cisco uBR7200 Series Universal Broadband routers, primarily designed for the cable core router product line. The new product is a hardware adapter and it can be plugged to the existing platform. It creates a combined solution of cable and wireless technology, which creates a hybrid networking solution.

Their variety and combinations can vary significantly from solution to solution, but here is another example of a hybrid solution, based on signaling and protocols, as initially designed for other technologies. It is called Cisco's Firestorm Multichannel Multipoint Distribution System (MMDS. This is a Broadband Fixed Wireless (BBFW) point-to-multiPoint (P2MP) headend (HE) and customer premises equipment (CPE) solution that is suited primarily for residential environments, which is designed to provide licensed broadband wireless access to a market not served by fiber or copper , which also will provide geographic coverage not possible with competitive unlicensed BBFW systems. For the HE, Cisco offers a wireless line card (uBR-MCW-MDA) which fits in a 7223 or 7246 uBR or VXR router, and a MMDS transverter (SX11127A) with duplexor. The CPE gear includes either a 951 router for data only or a 952 router for voice enhanced residential use. This BBFW P2MP solution operates at Layer 3, has non line of site (NLOS) capabilities (through the RF component), and can provide voice and differentiated services.

Extraordinary co-channel resolution and multi- path signal mitigation is based on signaling protocols QAM 64 downstream with OFDM modulation and 16 QAM upstream modulation schemes, plus optional spatial antenna diversity for NLOS at both the HE or CPE. Also, a co-channel resolution capability is offered with Data-over-Cable Service Interface Specifications (DOCSIS) for subscriber management.

Another solution involves using the licensed and license-free U-UNI spectrums with a fixed wireless solution and terrestrial OC-3 backbone. This alliance was announced by WiFi Metro, Inc. in April 2002. WiFi is a wireless ISP (WISP) that owns a network of over 50 wireless hotspot locations and Gatespeed Broadband, Inc. The wireless HotZone of WiFi Metro, which provides high-speed Internet access to subscribers within a fifteen-mile radius of a centralized Wireless Internet Point of Presence (WIPOP), is combined with the fixed wireless solution of GateSpeed. The 2.4-GHz licensed spectrum runs the IEEE 802.11 protocol. The 5.2-GHz license-free spectrum is used for U-NII, and these two spectrum bands support nationwide deployment. This solution is fully compatible with existing Cisco Aironet 350 series and Cisco 1200 Series products.

Satellite communications can use another approach to provide Internet access, such as the DOCSIS 1.1 standard. It is well known that the primary focus of the DOCSIS standard is cable modem service, but the standard can be used for satellite with a specially designed DOSCIS terminal for emerging Ku- band satellite systems.

Another example here is Sprint, who is using hybrid networks that are based on a proprietary cable modem network in the Bay Area. It is basically a cable modem system, which has been frequency shifted to operate over wireless; it has all the same bandwidth sharing issues as cable modems.

The list of examples is much wider and includes Frame Relay over wireless, L2TP, Multiprotocol Label Switching (MPLS), GRE-based Virtual Private Network (VPN) in fixed wireless networks, Point-to-Point Protocol over Ethernet (PPPoE), and L2TP to MPLS conversions for fixed wireless networks. The bottom line is that market conditions in the U.S. have proved that these types of hybrid solutions can be successful, based on the fact that they combine existing with emerging or evolving technologies and require less of an investment, which provides new solutions and covers more user -based demand areas.