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Telstra 4G Explained

4G - Telstra's next major infrastructure upgrade.

Initially available in major cities, airports and selected regional areas in October 2011, Telstra's 4G network offers significantly faster speeds, lower latency, and reduced network congestion. The latest upgrade to the Telstra 4G network and release of Category 4 LTE devices in February 2013 will see peak speeds of up to 150Mbps in Western Australia and selected areas.

The 4G network is based on LTE - 3GPP Long Term Evolution. LTE is a series of upgrades to existing UMTS technology and will be rolled out on Telstra's existing 1800MHz frequency band. This new network boosts peak downloads speeds up to 100Mbps and 50Mbps upload, latency reduced from around 300ms to less than 100ms, and significantly lower congestion.
Telstra LTE 4G modem

What does this mean for me?

Telstra 4G is advertised as available within 5km of CBD areas and airports offering speeds between 2Mbps and 40Mbps. When launched the network was limited to major towns and cities, but since late 2011 the network has expanded to include most major regional towns. The Telstra Next-G 850MHz network will no doubt remain the backbone of Australian mobile coverage, with LTE 1800MHz serving in high density residential and metro areas effectively creating a 'hybrid' network. Multi-mode and multi-frequency 4G modems such as the Telstra 320U USB allow seamless transition between 4G and Next-G networks when on the move, often a slight pause or delay is the most you'll notice when your modem switches over to the other network.

Which Cities and Towns?

View the official Telstra 4G location map below.

Rather than rolling out LTE in regional and rural areas, Telstra will likely opt to upgrade its infrastructure to Dual Carrier HSPA+ (up to 42Mbps) instead, due to the limited distance the 1800MHz frequency can travel. Having a much higher frequency than the 850MHz Next-G network drastically reduces signal penetration and range, resulting in coverage similar to that of competitor 3G 2100MHz networks like Vodafone Mobile Broadband.

Why 1800MHz

Given the big reduction in coverage you might be wondering why Telstra chose to deploy its 4G network on the 1800MHz band. Like most decisions the biggest factor governing the choice is money. Already licensed by Telstra, the underutilised 1800MHz network was previously used to provide 2G voice calling and text messaging services, and 2G EDGE data services (often indicated by the 'E' symbol on your phone). By converting this band from 2G over to 4G, the network can be deployed with drastically reduced cost and time to market. Instead of building new cell towers, the existing 1800MHz antennas could be swapped with antennas designed for MIMO LTE services and other hardware changes kept to a minimum.

The limited choice of available mobile spectrum means that for the next few years 1800MHz will remain the band of choice for 4G services. Around 2015 the 700MHz "digital dividend" band will become available and we can expect to see a much higher performing 4G network with far greater coverage, speed and signal penetration.

What about backhaul

With a massive increase in speed, how can the cell tower transmit and retrieve all this extra data from the Internet? Your 4G connection is only as fast as what the phone tower can provide you. Older EDGE or HSPA networks can get away with E1 or optical fibre backhaul links (ie the link that connects the tower into the wider network), but LTE services require a far more advanced Ethernet-based backhaul link. The transition from circuit-switched to packet switched (IP based) networks affords better QoS (through MPLS and other link/network layer protocols) and significant reductions in latency.

4G Antennas

If you've read this far you might be thinking the technology sounds awfully complex, but thankfully the complexity ends at the modem. 4G antennas are actually quite simple and follow the same principles that regular 3G antennas do.

Frequency

The primary difference is the frequency the antenna operates on. 3G and Next-G operate on a much lower band - 900MHz and 850MHz respectively, compare this to Telstra 4G which operates on the 1800MHz band. Having a much higher frequency than the 850MHz Next-G network drastically reduces signal penetration and range due to the higher density wave - a good comparison is AM radio compared to FM radio - the higher frequency FM radio contains a much higher quality signal but has significantly reduced range.

Because your modem needs to both transmit and receive, 4G requires two frequencies - one for transmitting and one for receiving.

Most areas in Australia 4G has a 15MHz bandwidth and operates on the following frequency ranges:
Tower Tx: 1805-1820MHz
Tower Rx: 1710-1725MHz

New South Wales and Victoria have a much smaller bandwidth of 10MHz and operate on the following frequencies:
Tower Tx: 1805-1815MHz
Tower Rx: 1710-1720MHz

4G bandwidth (ie the width of frequencies we can send and receive on) is critical in supporting high speed and a high number of users. Because in order for your connection not to get confused with someone else's, each user is allocated a small sliver of frequencies that they can transmit on and nobody else can. You'll notice this most during peak usage hours, where as more people start using the tower it will reduce the width of your (and everyone else's) sliver of frequencies, resulting in each person getting a reduced download/upload speed.
Naturally this is a very simplified explanation (for more info read up on OFDMA and SCFDMA) but for our purposes it will suffice.

MIMO

The second most important feature of a 4G antenna is the capability to operate in MIMO.
4G cross polarisation x-pol 45 135 degrees
4G uses a technology called MIMO "Multiple In Multiple Out" where your modem uses two separate antennas at once to deliver super fast speeds.

Normal 3G and Next-G signals are broadcast vertically polarised, where the wave travels "up and down". LTE MIMO waves are slant polarised where each wave is rotated 45 degrees from the horizontal, mirrored so the first is at 45 degrees and the other at 135 degrees. This smart little trick is called polarisation diversity and allows your modem to distinguish two independent streams of data over the same frequency allocated by the cell tower.

Because our modem has two internal antennas each responsible for receiving one stream of data, it is absolutely crucial we have two separate external antennas. We cannot use a 'Y' patch lead or some other trick to connect both ports of the modem into one antenna, nor can we connect both external antennas into one port.
4G LTE MIMO in low signal areas
It is important to know MIMO is switched on and off by the modem. The decision whether to use MIMO is negotiated with the cell tower, whereby the quality of the received and transmitted signals are assessed (a metric known as CQI). When signal strength or quality is low it's difficult for the modem to distinguish between the two data streams, so when signal levels drop below a certain threshold level, MIMO is switched off and the modem operates with only one antenna (Port 1 on Sierra Wireless modems).

Interference

The distinction between signal quality and signal strength is not to be overlooked. Strength refers to the total available power (amplitude) of the signal, ie how loud our signal is, whereas quality refers to the degree in which information can be correctly interpreted from the waveform. Thermal, gamma radiation and other systematic noise sources all impact the quality of our signal.

Different Types of 4G Antennas

Given all our 4G antennas are designed for 1800MHz and can be operated in MIMO (or already are in MIMO kits), what's the difference between them?

Antennas simply listen. Some listen to signals coming in from any direction, and others listen very intently but from only one direction. This 'listening angle' is referred to as horizontal beamwidth, and is an angle in degrees of the horizontal plane in which a signal can be heard. As you decrease the receiving angle, the intensity in which the antenna can listen increases - antenna gain represents this trade off between the width of the angle and the listening intensity. To make this more intuitive consider the following scenario.

Picture standing in a crowded bar, if an attractive woman were to walk up and talk to you, you might be able to hear her but the conversation wouldn't be great, you're probably going to get her name wrong. Now suppose you could block out the noisy people standing directly behind you - naturally your ability to hear what she's saying improves. Imagine then you could then block out the people standing to your left and right - the quality of conversation improves again. By repeatedly decreasing your 'listening angle' until you can't hear anyone else, the quality of conversation is now effectively perfect.

This analogy is not trivial. By decreasing our horizontal beamwidth we were able to eliminate sources of interference and background noise, and upon each successive reduction we reassessed channel quality, then reduced transmission power and renegotiated a more complex method of physical layer modulation to increase our symbol rate. In other words, we were able to make the transition from yelling "do you come here often", to having an engaging conversation.

4G 1800MHz LTE antennas horizontal beamwidth vs distance

Omnidirectional Antennas
This type of 4G antenna can listen from any direction (360 degrees), but achieves it's gain by reducing our vertical beamwidth - the height in which we can receive from, as opposed to the width). In the context of our bar example this would be the equivalent of not listening to the floor or the roof - this makes the antenna appropriate for just about all locations, unless of course the mobile phone tower is directly above or below you.

Panel Antennas
If we were to take our omnidirectional antenna and start folding back our 360 degree angle, decreasing it until about 65 degrees we vastly increase the ability to hear signal coming in from that angle. This type of antenna is often favoured because of it's no-fuss mounting, compact size, and very reasonable gain. Our 10dBi MIMO panel includes two antennas in the one weatherproof unit. The ability to point the antenna in the general direction of a 4G tower and obtain a signal makes the unit perfect for use around town and a few kilometres outside the 4G zone (usually less than 10km). While we've managed to operate panel antennas up to about 15-20km from the tower, speeds have been considerably less than those achieved by higher gain antennas at the same location, and MIMO disengaged.

Yagi Antennas
Taking our panel antenna and tightening the receiving angle till around 40-50 degrees we again increase the signal strength in the direction that our Yagi antenna is pointed. This type of antenna offers superior performance over the panel antenna and offers an interesting characteristic known as Front-to-Back ratio. An increased Front-to-Back ratio tells us that the antenna is much better at ignoring interfering signals that are behind the antenna - very important in city areas where there are often a series of cell towers in the immediate vicinity. A 4G Yagi antenna such as the 12dBi RFI Log Periodic Dipole Antenna is often used in areas where a reasonably wide receiving angle is required due to the presence of buildings or terrain that are blocking line of sight to the 4G tower. This LPDA antenna also has the unique capability of providing a high gain on all frequencies 700-3000MHz, in case 4G is unobtainable.

Grid Antennas
The 4G grid parabolic antennas are our most tested and trusted antenna for the Telstra 4G network. These have been used to achieve Australia's fastest 4G speed (89.3Mbps as of October 2012). The large grids provide an unmatched front-to-back ratio and tight receiving angle, which cut down background interference to provide an ultra clean signal. This is extremely important as a cleaner signal will allow the modem to negotiate a more complex (and faster) method of modulation. This antenna is suitable for all city areas and rural areas with good line of sight - if you have a hill between your location and the cell tower you are better off using a 4G Yagi. Grid antennas can be used out to 30-40km from a 4G tower if you have good line of sight (with some degree of freznel zone clearance).

So, which antenna do I need?

Selecting a 4G antenna depends on both the area you're using it, as well as whether you need a portable or permanent solution.

Around Town

If you can receive 4G outside or just down the street, or just need to increase speed, generally nothing drastic is required. Take a look at our convenient desk mounted 4G antenna for indoor use, or our compact Omnidirectional 4G MIMO Antenna for a high performance weatherproof roof mount antenna.

4G Antennas - Outside Official Coverage Zones

When connecting to 4G towers off in the distance you'll need a more substantial antenna. If you're confident in locking on to a 4G signal our 17dBi 4G grid antennas are used right around Australia - from mining and heavy industry, to commercial factories and residential houses. If you need a 4G antenna that can fall back on 3G/Next-G if 4G is not available or too weak the best antenna is our 12dBi multiband 3G/4G Yagi.