Wireless Broadband Technology Overview

This article provides a general overview of broadband wireless technologies.  It is intended to provide a high level understanding of wireless concepts to those with little or no wireless experience.

Wireless broadband technology is commonly defined as the transfer of high-speed data through the airwaves.  The technology has improved dramatically over the past 10 years and continues to improve significantly.  Wireless can be a cost effective solution for many communications applications such as Internet access, inter-office communication, video surveillance, and remote monitoring.  Wireless sometimes gets a bad rap for not being reliable.  However, most issues with wireless reliability are because the system was not designed or installed properly initially.  If designed and installed properly, wireless can be extremely reliable. 

Wireless Frequencies

The FCC governs the use of radio frequencies and carves frequencies into bands and specifies how the bands can be used.  These bands can be ‘Licensed’, ‘Unlicensed’, or ‘Lightly Licensed’.  The frequencies used for wireless communications are referred to by their number of cycles per second, called hertz.  Most are in either what is called the Microwave or the Millimeter Wave frequency bands, and referenced in megahertz (MHz) or gigahertz (GHz).  Click here for a table of the most common wireless broadband frequency bands. As a rule, the lower the frequency the further distance that can be obtained, but the lower the throughput capacity.  Throughput, is commonly referred to as speed, measured in megabits per second (Mbps).

Licensed, Lightly Licensed, & Unlicensed Frequencies

Unlicensed: Anyone is allowed to operate equipment in the unlicensed frequency bands as long as that equipment meets the FCC’s power and antenna specifications for the band.  The equipment must first be certified with the FCC, which is done by the manufacturer.

Systems in the unlicensed bands are quick to deploy and generally lower cost than licensed.

Unlicensed systems operating at 5GHz and below are generally lower cost and lower throughput than the higher frequencies.  Throughput typically ranges from 5Mbps to 20Mbps, but higher throughput is possible with other trade-offs.  These systems can also have limited non-line of sight capability.  Unlicensed systems are also available at 24GHz and 60GHz with much higher throughput, but short distances.

Licensed: With licensed frequency bands, an entity pays the FCC a fee in order to receive an exclusive right to use a frequency in a specified area.  The most notable examples are the cell phone companies who have paid Billions of dollars for the frequencies they use.  However, it is possible to get a license for a point-to-point link between locations for a reasonable fee.  Licensed radio systems are more expensive, but have higher throughput rates and are easier to guarantee reliability.  Links operating in the 6,11,18, & 23GHz bands can have distances ranging from 3 to 50 miles and a maximum of up to 300Mbps per link. 

Lightly Licensed: Lightly licensed frequency bands are somewhat of a hybrid of the other two types.  An entity must register with the FCC and pay a nominal fee before using any equipment operating in the band.  Although registration is required, it does not grant an exclusive right to use that frequency in any particular location.  Users must still work with each other to mitigate any potential interference issues. 

Point-to-Point

Point-to-Point wireless systems connect just two sites together.  They are generally used when relatively few, fixed locations need to communicate, but a high data throughput is needed, and reliability is critical.  Point to point wireless can be a very cost effective alternative to fiber or T-1 based services from the phone company.  Distances can range from a few hundred feet to over 60 miles.  The distance capability depends on frequency, antenna size, tower height, and radio power.  Data throughput rates range from about 5Mbps to 1Gbps.

Multipoint

Multipoint wireless systems are systems where multiple ‘client’, or subscriber radio devices communicate with a single, central radio, commonly called an Access Point or Base Station.  Multipoint systems are used where multiple sites or devices in an area need to communicate.  Cellular, WiMAX, and Wi-Fi wireless LANs are examples of multipoint systems.  The nature of multipoint systems with multiple remote devices sharing access to the central radio makes the method of how this sharing occurs a key factor in how the system performs.

Now imagine that you are trying to talk to two different people, one on your cell phone and the other on your office phone, so the two you’re talking to cannot hear each other.  Without your intervention, the two will talk at the same time and you won’t be able process what they are saying.  You will have to tell them when they can talk.  Outdoor multipoint wireless systems operate in this manner.  The remote subscribers cannot ‘hear’ each other and if they worked like Wi-Fi, they wouldn’t work very well if many of the remotes have much data to send.  With true outdoor multipoint systems, such as WiMAX & Motorola Canopy, the client radios must first make a request and have it acknowledged by the Access Point before sending data – Similar to raising your hand before talking in a big group.

Mesh Networks

Mesh Networks are basically groups of multipoint radios with additional software that enables them to relay traffic through each other to get it to its end destination.  By relaying data between radios, the network can get around line of sight obstacles.  For this reason, mesh networks are typically used in applications where mobility and near ubiquitous coverage is required.  The drawback of mesh networks are that they are more expensive than multipoint networks and performance degrades significantly as traffic is relayed through more than two or three radios.