Technology

5GHz vs. 2.4GHz

Technology

Which wireless networking technology best suits our needs – 2.4GHz or 5GHz? The answer depends upon several factors.

Operating in the 5GHz frequencies, our radios can utilise OFDM technology. This means that the radio uses multiple carrier frequencies within a given range to carry a large amount of data and multiplex the signals to reduce the effects of echo and interference on the transmitted signal.  In short this means that we can achieve high data rates and Obstructed Line of Sight (OLOS) connections between A & B over long distances.

In a normal 2.4GHz DSSS environment the multi-path signal is easily distorted by echoes, meaning the data is corrupted and frequently needs to be retransmitted, or more commonly the radios cannot associate at all.  OFDM radio transmissions do not suffer from echoes to anything like the same extent.

Line of sight …

One of the outstanding features of an OFDM radio operating in 5GHz is its ability to overcome obstacles such as rises in the ground, trees and buildings to connect networks together over long distances where no clear line of sight exists. Depending upon the geography of the land, distances of 15 to 50Kms are quite achievable in ETSI countries. Longer distances are achievable outside ETSI governed countries as higher levels of transmit power can often be used. 

Many manufacturers insist on describing their OFDM radio’s as Non-Line Of Sight. WIN prefers to more accurately describe the environment in which the OFDM radio's work as - Obscured Line Of Sight (OLOS). OLOS well describes the ability of OFDM to overcome obstacles which OBSCURE the conventional line of sight and Fresnel Zone needed by say a 2.4GHz radio.

So how does the OFDM radio achieve connectivity in OLOS applications?
Well, up to the point at which the radio energy hits an obstacle, it operates as if a point-to-point radio. However, at the point at which the energy hits the obstacle, it becomes in effect, a ‘multi-path’ radio and through reflectivity of the radio energy, the equipment at the remote end receives some if not most of the transmitted energy.

No Line of Sight? - No Problem!

One of the biggest problems facing WIN designers is the issue of line of sight. Traditionally it was an open and shut case; line of sight meant a wireless link can be achieved whereas no line of sight meant there could be no wireless link.  Using OFDM radios means we re-think these rules and predict the performance of a link where there is no clear line of sight.

OFDM radios when operated in Obscured Line Of Sight (OLOS) conditions work well in both in urban environments as well as in rural locations. 

Where line of sight is available the network is easier to design and predict data rates. Links of up to 50km with clear line of sight are possible in the UK using high quality OFDM radios.

Radio Agencies and 5GHz technologies

The release by Ofcom in the UK of the 5GHz - Bands A, B & C, enabled the deployment of Fixed Wireless Access (FWA) and connectivity to increase substantially. For example, in the UK, the 5.8GHz Band C (5.725 – 5.795 and 5.850-5.875MHz ) is allocated for use as Fixed Wireless Access (FWA)

This lightly licensed 5.8GHz Band C allows our network designers to increase the scope, range and size of their wireless solutions, all at low cost. Using Orthogonal Frequency Division Multiplexing (OFDM) radio technology our 5GHz equipment can provide a robust wireless connection even where there is no clear line of sight between locations.

We have been pleased to be part of the Wireless Advisory Group (WAG) and in particular the Radio Agency (Pre-Ofcom UK) committee which designed the UK’s IR2007 interface requirements standard. Recently Ofcom UK has released a new spectrum at 5.4GHz (Band B) frequencies for use as Fixed Wireless Access.

Elsewhere in the world, we provide wireless solutions based upon the 5GHz frequencies made available for use by the local Radio Agency.

2.4GHz vs. 5.8GHz Band C

5.8GHz band C OFDM is not a replacement for 2.4GHz radio links, but complimentary. WIN uses OFDM radio’s where either higher data throughput is required or where no clear line of sight between buildings exists. In both cases, the higher cost can readily be justified.

OFDM Overview

  • OFDM = Orthogonal Frequency Divisional Multiplexing
  • Carrier centers are put on orthogonal frequencies
  • ORTHOGONALITY - The peak of each signal coincides with the trough of other signals
  • The result is very high spectral efficiency

           
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Different types of OFDM

There are several different types of OFDM radio technology. Each presents a different performance and feature set. When setting out to design a solution based around OFDM, WIN specifies appropriate type of OFDM technology.

All OFDM radios are not the same

The performance and features of OFDM radios differ greatly and must not be thought of as being the same. They are not! There are three categories of OFDM radio available.

High-end, leading edge technology

  • Operates in very poor non-line of sight conditions
  • High data rates

General purpose

  • Operates in some obscured line of sight conditions
  • Medium data rates

Mass market & commodity

  • Poor operation in obscured line of sight conditions
  • Low to medium data rates

In summary, both 2.4GHz and 5GHz radio solutions can be deployed with equal success and is well designed, the solution will provide robust wireless network infrastructures. Your WIN designer will consider a number of factors before deciding on the appropriate technology to deploy as the wireless infrastructure, including - data rate, distance, interference, scalability, price, robustness and the all-important - line of sight.

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