Wireless Backhaul: The Ideal Solution for Wireless Internet Service Providers

There are many challenges that a wireless Internet service provider (WISP) must overcome to become a profitable business. Apart from commercial and management challenges, technology selection is critical to success, as the network enables the WISP to develop competitive advantages by delivering faster access and meeting customer’s needs.

With the focus on selecting the right access technology, many operators overlook another important part of their network--backhaul. Once customer traffic reaches the access point or subscriber hub, consolidated traffic needs to be reliably and cost-effectively transported back to switches and Internet gateway. These transmission links need to be reliable since they carry traffic from a large number of subscribers. Operators have the choice of a variety of backhaul methods, including owned fiber, leased copper T-1’s, and wireless, including licensed and unlicensed options.

The proliferation of WISPs is spurred by the lack of high-speed Internet access in suburban and rural areas available through more mainstream technologies such as DSL or cable and where traditional dial-up access just doesn’t satisfy the customer’s connectivity needs. The main segments addressed are residential customers and small-to-medium size businesses (SMEs). WISP service delivery ranges from “best effort” (95% connection time) access to the Internet to service offerings tied to contractual service levels (upload/download throughputs). WISPs falling into the latter category are focused on future-proofing their network infrastructure to handle expanding an customer base, increasing customer bandwidth requirements and the future delivery of enhanced services that may even include voice circuits in addition to Internet access. 

Designing a wireless network is a complex endeavor, often overwhelming. The first two steps of the design process include the site selection and system requirement identification. Both of these steps have great interdependency, as they constitute the core of the service delivery function. Selecting the right combination of technology is essential, but varies according to target customers. This choice can be mind-boggling--MMDS, 802.11a/b/g, 802.16, 802.20, etc. All these systems have a wide variety of range, capacity, line-of-sight (LOS) or non-LOS, depending upon the demographic of the target market and the operator’s business plan and objectives.

Fortunately for WISPs, the choices available for the backhaul network are much more straightforward. Depending on the network architecture and area covered, the backhaul may span up to a few thousand square miles. The choice of base station capacity dictates the backhaul options, so identifying complementary equipment vendors for access systems and the backhaul network is critical. 

Wireless systems provide a number of advantages over self-provided fiber, such as greatly reduced CAPEX and faster deployment, and T-1-leased lines for which operators are locked into high recurring OPEX (particularly in rural areas where many of these networks are likely to be located) and lack of direct control over the backhaul transmission network.Wireless backhaul itself comes in two basic flavors: licensed and unlicensed (also known as license-exempt).

Unlicensed systems operate in either the 2.4GHz ISM or 5.8GHz UNII bands, and have the benefit that they can be purchased off-the-shelf and installed by any person or organization at any time, with no requirement to prepare and file for an FCC license. But the main drawback is the potential for interference, which causes poor receiver performance and transmission errors or even total outages. By the very fact that the radio spectrum is shared with all comers, unlicensed radios are susceptible to interference from other operators. This is not usually an issue until the spectrum becomes very crowded as the radio techniques used are designed specifically for operation in a shared environment. However, at 2.4 GHz there are now many areas in the United States where overcrowding has resulted in unacceptable levels of interference, and the situation is certain to get worse with the continuing growth of off-the-shelf wireless LANs. By comparison, the 5.8 GHz band has been established primarily for radio communications, with more bandwidth available and is still relatively free of overcrowding. Even if interference-free transmission is obtained at installation, there is no guarantee that this will continue for the lifetime of the link operation.

In addition, most unlicensed radios do not provide options for hardware redundancy for very important customer traffic. In summary, unlicensed radios are rarely considered for “Carrier Class” applications. 

Licensed radios communicate using a user-assigned frequency channel, which is coordinated with other users in the same geographical area to ensure there is no potential for mutual interference. Licensed microwave networks rarely suffer from interference, but in the event they do, it is usually resolved with FCC assistance. Operators thus have peace of mind in the knowledge that the assigned channel is for their exclusive use within its geographical area, and that critical communications are unlikely to ever be disrupted by interference from other operators.

With licensed systems, a much wider variety of choices is available, from frequency bands including 6 and 11GHz (where link distances of 60 miles and longer can be achieved) to the other “common carrier” bands of 18 and 23GHz for shorter links up to 20 miles. Capacity choices are also available from a few T-1s, DS3, and all the way up to multiple OC-3 (Nx155Mb). But the protection of licensed operation comes at a price, in terms of the FCC License Fee, as well as the inconvenience of the application preparation, Prior Co-ordination Notice (PCN) and lengthy FCC processing time, which typically takes between seven and 10 weeks, though actual link operation can commence after three weeks with expedited PCN or five weeks under normal circumstances.

A WISP network is all about bandwidth and IP services, which should drive the process of equipment selection. Operators should plan on having enough bandwidth capacity to enjoy success, instead of finding out too late that bottlenecks were designed into the network. If overcapacity is a concern, then selection of a system that has a small startup cost and a linear incremental cost can be made, enabling the network to grow along with customer requirements, using equipment that can provide smooth capacity expansion.

Whether you are interconnecting a number of MMDS base stations, delivering high-speed Internet access or deploying a LAN extension, the wireless equipment must handle Fast Ethernet today and enhanced services in the future--equipment that is optimized for voice applications and carries data efficiently is an ideal solution.

Licensed wireless backhaul is a proven solution for providing connectivity between base stations and access points in fixed and mobile wireless access networks. In particular, emerging WISP and MMDS networks throughout the U.S. can benefit from the fiber-like reliability and availability of licensed wireless, providing transmission links over large distances and difficult terrain where alternatives like cable or fiber are not feasible alternatives. Modern licensed wireless systems are also very suitable for the transport of IP data traffic, either alone or in conjunction with voice services, with a higher degree of protection than normally provided by data-only networks and very low latency.

Louis Samara is the product marketing manager at Stratex Networks and can be contacted at Louis_samara@stratexnet.com.

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