Tuesday, 25 June 2013

NBN for Real People: "Wireless"

"What is Wireless?" Part of a series on NBN topics written for "Real People".

The "Wireless" in NBN Co's "Fixed Wireless" is a mobile phone service, currently "4G" or LTE, working with fixed, not mobile, devices to a distance of 30km.

This is very different to the "wireless" your laptop & tablet use to connect to your home "wireless LAN", sometimes written as WLAN.

These are different from "Bluetooth", also wireless, but very lower power, very short range and low speed. Good for headphones, loud-speakers and keyboards.

"personal hotspots" provided by smartphones are worth noting here. The allow other local devices to access the Internet via the (wireless) Mobile Phone network of the smartphone.
The iPhone can share it's connection via USB (cable), WiFi or bluetooth. USB is fastest and consumes the same or less power than bluetooth. WiFi is ten times faster and longer range than bluetooth, but "will drain your battery". Speed and power are usually related: more power needed to go faster.

NBN Co chose to use expensive and slower Fixed Wireless only in situations where it was more "cost-effective" (cheaper) to do so. The cutoff was around $5-7,000 per premise. Mobile phone technology has many limitations, not only substantial towers, noise + interference and lower speeds, but a single channel shared between all users talking to the one base station. A "cell" is the roughly circular area around a base station. Large areas are covered by a mosaic of overlapping "cells". Calls can be automatically transferred, or "handed off", between base stations of adjacent cells as handset moves around. Driving, or walking, down the road, you can continue a call without pause as the base stations successively hand-over from one to one another. This means a call can be cutoff if the cell you move into is "full" and cannot handle any more calls.

A Fixed network doesn't have to deal with hand-overs as customer devices never move.

100Mbps may be achievable without error correction, right by the tower for just one person, but in high-traffic, high-revenue areas where active calls might be in the hundreds, congestion, and terrible throughput and high-latency for everyone, results.

The engineering solution is as expensive as simple: create more cells by increasing the number of base stations.

Your "wireless LAN" is also called WiFi but its full title is "Ethernet over Wireless", defined in a series of IEEE standards numbered 802.11. There have been many variants (802.11a, g, n, ac, ...) increasing notional rate ('speed') from 11Mbps (11b) to 300Mbps (11n) and soon a potential 1.3Gbps (11ac).

They have used two bands, 2.4Ghz & 5Ghz which like "CB" radio, are free to use ("unlicensed" or 'Medical and Scientific Instruments') but only if very low power is used:  1 watt effective radiated power (ERP) in Australia, as I understand it. These frequencies are very crowded, and a new standard, 11ad, will optionally use 60Ghz. Do not expect this to penetrate walls - if there isn't line-of-sight between the aerials of the two devices, it can't work.

Wireless LAN's are unlicensed, unregulated, short range (20-30m), "line of sight", low-power and mainly used indoors. Enthusiasts have achieved one-off connections with specialist antennas of 100km.

Mobile Phone, which use 4 different bands, 700Mhz is latest to be released in Australia.
 900Mhz 1800Mhz & 2600Mhz are the current frequencies licensed to mobile network operators.

Mobile Phone networks have:
  • higher power
  • long range per cell (10km or more)
  • use expensive licensed spectrum.
  • may have many people competing to use a cell, leading to congestion.
A Brief, unreliable history of Cellular Mobile Phones.
  • AMPS - Analogue Mobile Phone Service came first. the 'bricks'. Developed by Motorola, they invented "cells" and automatic hand-overs between base-stations.
  • 1G - Digital Mobile was GSM (Groupe Special Mobile): an ITU standard. Worked with something called TDM - Time Division Multiplexing - with 8 fixed time slots on a single frequency, giving a hard distance limit (light takes time over distance).
  • 2G -Digital Mobile was CDMA from Qualcomm. "Collision Detection Multiple Access". Evolved into EVDO, then was abandoned.
  • 3G -Digital Mobile... The majority of networks now.
  • 4G - Digital Mobile, also called LTE - Long Term Evolution.

Other resources:

Wikipedia on 4G in Australia:
http://en.wikipedia.org/wiki/4G#Australia and http://en.wikipedia.org/wiki/4G_Australia

and 3G
http://en.wikipedia.org/wiki/3G and a variant http://en.wikipedia.org/wiki/HSPA%2B

NBN's Wireless factsheet.

A good consumer guide to look through. Pictures of things that matter, from 2011.

NBN Co Technical Design Rules. Up to 60 premises per sector, 3 sectors per tower, sharing 100Mbps.
Elsewhere, a claimed hard limit of 11kms on LTE in TDD mode used by NBN Co.

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