1/9/08 - The topic of much debate, WiMAX is rapidly becoming a growing market. With more service providers and enterprises jumping on the WiMAX bandwagon, the next step is to accelerate the deployment of WiMAX worldwide by leveraging the numerous benefits of wireless backhaul.

So, what's all the hype about?

WiMAX or Worldwide Interoperability for Microwave Access was developed in 2001 by the Institute of Electrical and Electronics Engineers (IEEE), and has been defined as a "last mile" broadband wireless access alternative to services, such as cable and Digital Subscriber Line (DSL). WiMAX carries high-speed data connectivity to wide coverage areas, opening up ubiquitous "always on - anytime, anywhere" Internet and mobile access.

2007 trends show the WiMAX market continues to grow. In March 2007, Infonetics Research estimated the worldwide WiMAX equipment market will increase more than ten-fold between 2006 and 2010, reaching almost $5.6 billion. Mobile WiMAX alone is forecast to grow to $3.7 billion in 2010, a five year compound annual growth rate (CAGR) of 201%.

As companies, such as Sprint Nextel and metropolitan areas, like Chicago and now New York continue to invest in this innovative technology, WiMAX is clearly a technology of the very near future.

What's backhaul got to do with it?

Although much attention has been dedicated to access elements of WiMAX networks, little focus has been placed on the wireless backhaul evolution. Wireless backhaul and the aspects of the technology are critical building blocks in the implementation of any WiMAX network topology.

WiMAX Backhaul is the transport link between a Base Station (BS) and the WiMAX Access Service Network Gateway (ASN-GW). Backhaul is generally defined as the network components which connect client/subscriber access sections of networks with their core switching and management topologies. It transports considerable traffic from a POP to the rest of the network, and essentially acts as the "glue" that pieces all of the network elements together. This enables the network to deliver seamless and transparent broadband communications to its customers effortlessly, with high reliability and availability.

For service providers who select WiMAX as their underlying technology, high-capacity backhaul is essential for ensuring continuous delivery of rich media service across high-speed data networks. If backhaul and its components are not cost-effective, resilient, scalable and able to supply sufficient capacity then a providers' entire network can be seriously compromised - resulting in significant customer churn.

Components of WiMAX Backhaul Architecture

The backhaul of the network is recognized as a major enabler of network performance. To deliver the expected bandwidth requirements of WiMAX and other newer technologies, the backhaul is critical.

Following is a list of the most critical requirements which must be addressed by any effective WiMAX backhaul architecture:

1. High-capacity - Rich media services enabler
2. Native Ethernet - WiMAX-inherent data architecture/structure
3. Accelerated and Rapid Scalability - Fast-time-to-market new service/solution design
4. 99.999% Availability - Real-time, critical services
5. QoS - Multi-service environment
6. Ultra low latency/jitter - Uncompromised, clean delivery of voice/video communications
7. OPEX and CAPEX Efficient - 4G business model success realization
8. Coverage - Mobile broadband requires better coverage, (something that wire line connectivity only to a base station cannot provide)

Backhaul Options

A good game plan for the development of WiMAX solutions is to examine the mobile carriers' business model and learn from their network considerations. Usage of technologies for backhaul is dependent on regional factors, including regulation, fiber reach and competitive environment. This being the case, one might also expect to encounter similar trends when transitioning to 4G mobile - whether WiMAX or any other technology. Overall cost of bit-per-distance, target network capacity and traffic type (all IP, TDM, or both) are the main factors impacting the selection of a backhaul solution.

While either wireless or wireline technologies can be used to build these backhaul systems, it's obvious today's cost factors almost prohibit the use of wired technologies to construct a WiMAX backhaul infrastructure.

For instance, the cost of deploying one mile of fiber in an urban environment can run from $250k to $1 million. Bridging the same distance using wireless microwave link would cost less than $50k to set up. The dramatic differences in pricing are mostly due to the continued high costs of deploying fiber along with the availability of fiber, which keeps costs significantly higher, and requires service providers to search for alternatives.

Though copper T1 lines might cost less, they have limited capacity of only 1.544 Mb. Even if a carrier uses four T1s, the maximum bandwidth they are able to support is 6 Mbps. This falls far shorter than the bandwidth that will be required by future WiMAX networks. Currently T1 is a cost-effective solution with an average cost per T1 standing roughly $400 (depending on purchasing agreements and geographical location). However, if a T1-based network needs to support higher bandwidth - in the tens and even hundreds of Mbps - the added copper lines multiplied by the cost per-line renders the technology uneconomical.

In contrast, wireless backhaul solutions can offer data rates reaching up to 900Mbps over a single radio channel. And, wireless links can be deployed quickly - where limited or no infrastructure is in place - eliminating the costs associated with digging up the ground to lay fiber or copper.

Looking to save capital expenditure associated with deploying fiber or even copper, WiMAX carriers often rely on existing infrastructure, leasing lines or fiber capacity from their competitors (i.e. the incumbent carriers). By setting up their own wireless backhaul links, WiMAX players reduce OPEX while minimizing their dependency on the competition - another significant benefit for WiMAX carriers.

With these examples in mind, and due to its rapid implementation cycle and scalability, it's clear that wireless backhaul is the most reasonable, cost-effective solution for WiMAX backhaul networks.

WiMAX Connected

WiMAX radios and microwave are two of the options to consider in deploying wireless backhaul. Since WiMAX was originally designed as a Point-to-Multipoint (PMP) technology with inherent overheads, it is costly and tends to consume large amounts of precious spectrum resources. Hence, the choice for microwave makes perfect technological and economic sense.

Deploying and managing microwave backhaul is simpler than ever. Although microwave backhaul requires the carrier to buy licensed spectrum, airwaves are generally available. Microwave backhaul systems have been designed to deliver 99.999 percent availability, and since they're built upon the reliability of the equipment and rapid recovery of wireless links, microwave requires less man power - allowing total costs to be extremely low.

As the second option, as service provider's shift from fixed to Mobile WiMAX, microwave radio is the natural backhaul solution. Mobility tends to dictate the need for greater coverage, and microwave radio enables service providers to obtain optimal coverage.

Currently, more than 275 WiMAX trials are in the process of evolving to OPEX/CAPEX sensitive mass deployments. Microwave also fits this need as it's a cost-effective, almost instant backhaul solution.

The Case for Ethernet

Combining wireless Ethernet over microwave is ideal for WiMAX backhaul. Apart from its inherent scalability features (unlike the rigid structure of T1 or STM connections) and support for ultra-high data-rates, Ethernet makes for "flatter", more cost efficient network topologies.

Ethernet backhaul can be used either by mapping Ethernet over a PDH/SDH connection, or by employing native-Ethernet solutions. The advantage of native Ethernet is that packets are not mapped into fixed length frames, such as SDH virtual containers or PDH frames. Instead, packet traffic is enabled using the smallest possible overhead and with an optimal frame size for each throughput and modulation scheme. At the same time, TDM interfaces are maintained to coexist within the same frame.

What does the future of WiMAX backhaul hold?

WiMAX is a versatile technology, enabling different service providers to offer compelling voice, rich media and data-oriented services in fixed, nomadic and down the road - mobile modes of operation. It fits the strategy of incumbent Telcos, cable companies, satellite operators and broadband ISPs without a wireless play to extend their services in cities and rural areas. At the same time, mobile operators consider WiMAX as their underlying 4G technology. Recent announcements from Sprint and Korea Telecom as spearheads demonstrate this trend.

Meanwhile looking at the global landscape of telecom infrastructure, it's clear that wireless backhaul will accelerate the deployment of WiMAX worldwide by improving the business case of both competitive service providers and incumbent's rural operations.

Wireless microwave backhaul provides bandwidth flexibility the WiMAX industry has been missing. Microwave backhaul will enable WiMAX in multiple scenarios, and will continue to drive mass acceptance in those places where fiber is either too expensive, or is unavailable. We are seeing this already in areas like Eastern Europe, Africa and throughout the Asia-Pacific regions.

The combination of very cost-effective wireless backhaul solutions coupled with the impact and enthusiasm for more bandwidth and more premium services will deliver a worldwide impact. It will increase coverage, raise the available bandwidth per user and lower the cost of operations, essentially leading to more successful WIMAX deployments worldwide.

About the author:
Aviv Ronai, Chief Marketing Officer at Ceragon Networks, has over 15 years of experience in the telecommunications industry. Having held a number of managerial positions at ECI Telecom, including Vice President of Marketing and Communications, Mr. Ronai also served 7 years in the Israeli Air Force as a telecommunication officer and held several project management positions. Mr. Ronai holds a Bachelor's degree in Electrical and Electronics Engineering and a Master's Degree in Business Administration from Tel-Aviv University.