Deploying Citywide Wi-Fi Networks
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Many municipalities, including big cities such as Philadelphia and San Francisco, are in the midst of deploying Wi-Fi networks that provide connectivity throughout most outdoor areas. With signal coverage over dozens and even hundreds of square miles, these systems are expected to serve a diverse set of applications, such as wireless meter readers, public safety, and traveling businesspeople. The creation of these systems offers significant value to city governments and the public.
Because of the magnitude of these wireless systems (as well as the considerable public attention), its very important that cities adhere to proven methodologies geared for large-scale wireless network deployment. This means using classical system engineering with special provisions that apply to the wireless nature of the solution. The following are important steps and tips that cities should follow:
- Requirements Definition. The deployment of any citywide wireless network should begin with a careful analysis of requirements. Start by identifying who will be using the network and the applications that they will utilize. For example, there may be a business need to enable wireless meter reading because it can significantly lower operating costs for the city. Also, city inspectors may strongly benefit by having wireless access to work orders in order to work more efficiently. Something else to consider is whether the network will provide public access to the Internet. After defining who will use the system, then describe additional specifications, such as supported security protocols, performance, battery backup provisions, etc. The city will need to include all of this in a request for proposal (RFP).
- Business Analysis. With requirements well understood, its time to look at the return-on-investment (ROI) potential of the system once its installed. In most cases, a city council will need to clearly see that the system will recover the costs related to deploying the network within an appreciable period of time, such as three or five years. Be aware, however, that youll probably encounter one or more naysayers who will try to derail the network deployment by targeting weak ROI analysis. Be sure that you have strong benefits and carefully identify the costs. A lot of this is mitigated by putting the burden of deployment and network management on the vendors, of course.
- Pre-Installation RF Survey. Citywide wireless systems operate mostly outdoors, and its very important to know whats lurking there before getting too serious about moving forward with the deployment. The main idea is to measure wireless activity in the bands where the system will operate, such as 2.4-2.5GHz and 5.0-6.0GHz.
Be sure to perform this testing at ground level where users will access the network and on rooftops where backhaul components will be located. Ive performed these types of surveys for large cities such as San Francisco, and Ive found that the there are thousands (and thousands) of existing Wi-Fi networks. They are likely inside homes and offices because the signal strengths measured from the streets are relatively low. The majority (75%) of the access points are operating on channel 6, the common default channel for 802.11b/g wireless LANs. By avoiding channel 6, existing wireless LANs will probably not have much impact on a citywide 802.11b/g Wi-Fi network. However, noise in the 2.4-2.5GHz band from non-Wi-Fi systems will likely be a source of RF interference and impact the selection of technology and mesh node density estimations. In some cases, where noise levels are very high or there are significant obstacles such as irregular buildings and structures, that may cause excessive multipath, it may also be worthwhile to perform some pilot testing.
Because conducting a pre-installation survey may put roadblocks in the way of a citywide deployment, a city shouldnt have the survey performed by any of the companies selling the system to the city.
- Mounting Asset Assessment. Citywide Wi-Fi networks have mesh nodes that installers distribute throughout the city by mounting them on street lights and traffic light poles. Take a close look at the availability and condition of these mounting assets. Be sure that they are still in good shape and can support the weight of a mesh node (about 15 pounds). Ive seen street light poles that have lots of rust and have been deemed unsuitable for the installation of mesh nodes, which should be mounted near the end of the arm for maximum signal coverage along the street. Also, identify the available electrical voltage, which may limit your selection of mesh nodes. For backhaul links, which connect the mesh nodes to centrally located controllers and head ends, survey rooftops that are available for use by the city.
System Design. This is a step that depends highly on requirements. A city will likely need to work with a wireless integrator, selected through a bidding process, in order to fully realize a solution. From the citys perspective, be sure that the integrator takes into account all application requirements, knowledge gained from the pre-installation survey, and understanding of available mounting assets.
- Acceptance Testing. After the integrator installs the system and deems it ready for use, the city should independently perform acceptance testing to determine if the system fully meets contracted requirements. This means conducting tests that verify compliance with signal coverage area, performance, security and operational support. This step is crucial to ensure that the system fully meets requirements and avoids future legal action between the city and the integrator.
Keep these tips in mind, and youll have a more successful experience deploying a municipal Wi-Fi network. Just dont forget that these systems are based on radio waves, which requires specialized testing to make sure the resulting system does what its supposed to do.
Jim Geier is the principal of Wireless-Nets, Ltd., an independent consulting firm assisting companies and cities with the implementation of wireless network solutions and training. He is the author of the books Deploying Voice over WLANs (Cisco Press), Wireless LANs (SAMS) and Wireless Networks - First Step (Cisco Press).