4G - LTE-Advanced

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 4G network is based on LTE-Advanced - 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. For more technical details on peak 4G speeds check out our fastest 4G speed guide.

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

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

When will I get 4G?

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, with plans to cover about 66% of the Australian population by mid-2013 by deploying 1000 new base stations.

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.

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.

MIMO

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.

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).