Flexible Architecture Enhances and Extends Today’s Services
The primary consideration in the network architecture design of the xMax system is to achieve the goal of providing reliable, resilient and secure voice and data services to fixed and mobile subscribers—at a fraction of the cost of traditional approaches. The system uses a proprietary over-the-air waveform that has been optimized for xG’s sensing-based cognitive radio. While based on Orthogonal Frequency-Division Multiplexing (OFDM), xG’s unique and patented protocol outperforms WiFi, WiMax and traditional cellular technologies like LTE in shared and interference-prone radio bands. In addition to its proprietary and highly optimized over the air protocol, xMax offers several unique and valuable capabilities not found in other cognitive (and traditional) radio networks. These include its all-IP (Internet Protocol) architecture, as well as its support of commercial smartphones, laptops, tablets and other WiFi and Ethernet capable Internet appliances via the xMod personal hotspot. A sample reference model of the resulting Internet Protocol (IP) centric network architecture is shown in Figure 1.
As the diagram indicates, the network architecture includes the following elements:
- A proprietary xMax over the air-interface designed for cognitive radio operation in unlicensed as well as licensed bands.
- xMod fixed and xVM mobile hotspots that bridge WiFi-enabled commercial smartphones, laptops, tablets and other Internet ready devices to the xMax cognitive network.
- xAPs, which provides wide area connectivity to end users devices via xMods. The xAP is a compact, single channel access point optimised for cognitive radio operation. Up to 18 xAPs can be co-located to provide up to 108 Mbps of total data in the 900 MHz ISM band. xMax channelizes the 902-928 MHz band into 18 discrete channels, which are only used when there is traffic to mobile devices that are registered with a particular channel.
- Access Network Gateway (ANG), called the xMCC in an xMax network that provides call process, IP packet delivery services and several other IP, mobility and network signaling related functions.
- Technology-agnostic backhaul links from xAP sites and the ANG (Fiber, Metro Ethernet, PTP Wireless, etc.).
Note: Radio spectrum utilization is highly efficient in that the system occupies only that spectrum which is necessary for individual data streams. The bandwidth of each channel is 1.44MHz with sufficient guard band between channels.
While the xAP appears conventional in both architecture and functionality, it provides flexibility, scalability and reliability not found in conventional mobile or WiFi-based wireless networks. The ANG (xMCC) is a novel piece of wireless infrastructure equipment that consists of 100% off-the-shelf hardware with proprietary software developed by xG:
- Ethernet Switch which aggregates xAP links.
- Firewall which provides private to public network address translation (NAT) services.
- SIP Proxy Server which supports SIP call control, xG’s SIP message compression technology, and E911 services.
- Proxy DHCP Server which is used for IP address services.• Network Monitor (xMonitor) software which is responsible for end-to-end network management and monitoring services.
Among the unique characteristics of the xMax network architecture is the way mobility is implemented. The system provides soft handoffs with make-before-break capability (timeslots are acquired before breaking a connection), which result in reliable roaming and a seamless user experience. With all handoff decisions made at the xMod level via proactive channel scanning, there is no need for inter-base station (xAP) communication, which helps drive seamless operation.
The architecture further supports low-cost service deployment objectives by leveraging commercial off the shelf (COTS) voice over IP (VoIP) equipment, software and services within the xMCC. The VoIP core contained within the xMCC consists of the following elements:
- SIP Proxy Server which provides traditional SIP call control services.
- Media Gateway – which provides media transcoding between IP and PSTN networks and is responsible for subscriber accounting/billing, PSTN call termination, “Direct Inward Dialing” (DID) phone number maintenance, voicemail services, and inter-network call signal routing, among others.
- The VoIP core can be owned and operated by the xMax operator, or can be provided as a third party service.