SISO stands for Single Input Single Output

In a SISO system a single antenna is used for transmission and reception. SISO is typically used in radio, satellite, GSM and CDMA systems.

SISO datalink

The antennas perform the activity of both transmitting and receiving the signal in order to establish the datalink. A typical MANET SISO datalink will achieve a throughput in the region of about 20Mbps. The legacy Wave Relay® MPU4 radio is an example of a SISO radio.

MIMO stands for Multiple Input Multiple Output.

The Wave Relay® MPU5 is a next generation MIMO radio.

In a MIMO system, multiple antennas are used for transmission and reception. MIMO systems achieve much higher data rates because of a technique used to transmit data simultaneously across multiple antenna. This technique is called spatial multiplexing.

MIMO datalink

The use of multiple antennas in a MIMO system provides other benefits. The ability to make use of multiple antennas, each one at a slight angle, provides increased performance and resilience – this is commonly referred to as antenna diversity.

Antenna diversity benefits your datalink by effectively giving the antenna a different “viewpoint” to its peers. Where antenna 1 might be susceptible to interference because of its angle (polarisation), antenna 2 and 3 might not be as influenced by interference because of their slightly different polarisation.

To help explain, a good analogy of antenna diversity is like looking at the same geographical landmark from 3 different angles – you might see more of the landmark at slightly differing perspectives.

Another technique employed in MIMO technology is space-time block coding (STBC).

Space–time block coding works in conjunction with spatial multiplexing, and is a MIMO technique used to transmit multiple copies of the same data across the three antennas and to exploit the various received versions of the data to improve the reliability of the data transfer.

Data transmitted via radio waves between two points has a particularly difficult journey. Every time a radio signal encounters a building, a wall or other obstacle, the RF signal basically inverts and fades. When using a 360° omni-directional antenna, this happens a lot!

These constant reflections and refractions of the RF signal are a form of interference. Each bounce of the signal reduces its overall clarity. Sending the same data three times (once per antenna) means that some copies of the received data may be closer to the original than others.

This redundancy results in a higher chance of being able to use one or more of the received copies to correctly decode the received signal. Space–time coding combines all the copies of the received signal in an optimal way to extract as much information from each of them as possible.

The Wave Relay® MPU5 radio uses these MIMO techniques to provide the most efficient, most advanced MANET system currently available.

The advantages of a MIMO datalink over a SISO datalink include:

• Increased throughput: Wave Relay® MIMO offers speeds of over 120Mbps  (5 times faster than SISO) for multiple streams of multicast HD video, 32+ voice talk groups, and data.

• Increased range: Wave Relay® MIMO is less susceptible to interference, and therefore has a better signal to noise ratio. This effectively means that the signal can travel further.

• Increased coverage: 360° coverage of high-throughput, long distance data

• Redundancy: Wave Relay® MIMO has three antennas and uses a combination of spatial multiplexing, space-time block coding and antenna diversity techniques to ensure the signal has the best possible chance of reaching its destination.

• Resilience: Less chance of interference means a more reliable link

• Improved overall performance: 5 x the throughput and 4 x the range of SISO systems

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A Mobile Ad-hoc NETwork (MANET) is a data network suitable for voice, data and video traffic. The network is ad-hoc because it is not reliant on any pre-existing infrastructure. Data traverses the network by ‘hopping’ from one network node to another until it reaches its destination.

Instead of using a centralised router, each node in the network participates in routing network traffic by forwarding data for other nodes. The determination of which node forwards the data is a dynamic decision made by the Wave Relay® algorithm based on a number of variables, including;

• Node availability
• Link status
• Environmental interference
• Network neighbour status
• The ratio of Signal (data) to Noise (interference)

Wave Relay® MANET networks are self-forming, self-healing. If nodes in a Wave Relay® MANET network become unavailable for any reason, the Wave Relay® algorithm running on the remaining nodes will reroute network traffic seamlessly via the most efficient path.

How does a MANET differ from a MESH network?

A MESH network is designed to be geographically static and is heavily reliant on a fixed infrastructure. Typically, a MESH network has one node designated as the ‘Master Node’ to maintain the entire network. This Master Node distributes DHCP network addresses to all other nodes in the network, and monitors the flow of traffic to decide on the most efficient route. The whole MESH network is dependent on this Master Node.

MESH Network – A Master Node is required at all times to maintain the network.

The Master Node in a MESH network is a single point of failure. What happens to a MESH network if the Master Node ceases to work…?

MANET networks are entirely dynamic and use an adaptive routing approach. There is no Master Node required to manage the network. All of the nodes in a MANET collaborate collectively to route traffic and maintain a robust link. This makes MANET networks much more resilient than MESH networks, and much less prone to failure. The ability of a MANET network to support this seamless transition of traffic essentially means the network is self-forming and self-healing.

MANET Network – Many more paths for the data, and no master node required.

A Wave Relay® MANET network operates at the OSI Layer 2 level – the same layer as a network switch. This provides the user with a ‘transparent network’. The IP address scheme of your MANET network doesn’t have to be the same as that of the devices connected to it, providing an almost plug-and-play experience. A Wave Relay® MANET network is essentially like having a really long Ethernet cable!

How does a MANET network differ from a WIFI network?

Quite simply, a WIFI network is a MESH network. One WIFI device (Node) speaks to another WIFI device (Node) via a router (Master Node). WIFI networks are dependent on routers to route their traffic.

How does a MANET network differ from a WIFI network?

Theoretically, a Wave Relay® MANET network will support an unlimited number of hops.

How many nodes can you have in a MANET network?

There is no limit to the number of nodes in a Wave Relay® MANET network. During real-world testing of the MPU5 MANET radio in 2018, a flat network of 320 MANET nodes was successfully evaluated with plenty of overhead for further expansion.

What does this mean for the user?

A Wave Relay® MANET network is ultra-reliable. Whereas MESH and WIFI networks are very static, MANET networks can adjust themselves on-the-fly to adapt to ever-changing operational environments.

Wave Relay® MANET networks are highly scalable, providing transparent seamless operation when nodes join or leave the network.

Wave Relay® MANET networks;

• are very easy to set up
• are self-forming / self-healing
• support adaptive routing
• are highly scalable – create networks with hundreds of nodes
• support an infinite number of hops
• seamlessly allow nodes to join or leave the network without network disruption
• are transparent – operates at the OSI Layer 2 level
• are mobile – MANET networks don’t require any fixed infrastructure
• have the ability for each node to optimally configure its transmission parameters
• support multicast traffic
• operate on 3 x 3 MIMO principles for high performance data rates

Radio signals are transmitted and received using an antenna. An antenna can be mounted vertically, horizontally, diagonally, or in a combination of orientations.

Essentially, the orientation of the transmitter and receiver must match in order to get the best possible signal. For every degree of separation that the transmitter and receiver are out of alignment, signal loss and noise start to occur within your datalink.

For the best possible datalink, you will want the strongest signal with the least amount of interference (noise) – this is referred to as the Signal-to-Noise ratio (or SNR). The higher the SNR, the better.

A vertically polarised antenna at the transmitter communicating with a vertically polarised antenna at the receiver will provide a good, clear signal. Lots of signal, low background noise.

A vertically polarised antenna at the transmitter communicating with a 45° slant polarised antenna at the receiver will provide a poor signal.

A vertically polarised antenna at the transmitter communicating with a horizontally polarised antenna at the receiver will provide no signal.

The antenna images above are for illustrative purposes only. It should be noted that antennas can be electrically polarised in a different orientation to their physical appearance. For example, the new Wave Relay ANT-2037 horizontally polarised antenna is physically vertical in appearance but transmits and receives an electrically horizontally-polarised signal.

Wave Relay ANT-2037 Horizontally Polarised
Antenna

Wave Relay ANT-2005 Vertically Polarised
Antenna

Why not have all three antenna always vertically polarised then?

Because there are lots of environmental and other unseen RF interference’s operating in the same frequency space as the transmitter and receiver over which you have no control. This interference is inevitable and not something that can be easily prevented. RF airspace rarely exclusive, and you are likely to have to share your RF space with other users, such as mobile phone network operators, TV broadcast operators, WIFI hotspots, etc. Just like your own datalink, these other RF signals will have a polarity – some will be vertical, some horizontal, some diagonal, and various degrees of separation and combinations of each.

The interference is likely to differ in each and every scenario. In some environments, vertically polarised antenna might be more susceptible to interference than horizontally polarised ones (because there might potentially be lots of other vertically polarised transmitters & receivers within the local vicinity, for example).

What is antenna diversity and how does it help?

The Wave Relay® MPU5 radio has three antenna ports. These antenna ports can be used to connect different polarity antenna giving your data the best possible chance of reaching its destination.

The Wave Relay® MPU5 radio in this image is fitted with two ANT-2005 vertically-polarized antennas, whilst the centre antenna has been replaced with an ANT-2037 horizontally-polarized antenna.

Because the Wave Relay® MPU5 makes use of spatial multiplexing and space-time block coding MIMO techniques, the same data is sent three times (once per antenna) and re-assembled at the receiving end of the datalink.

If there is interference on the horizontally-polarised antenna, data sent via the vertically-polarised antenna still has a very good chance of being received.

In field tests, having an antenna combination such as this has proven to almost double the bandwidth of the datalink.

Note that the two ANT-2005 antennas aren’t entirely vertical, but slanted. Again, this antenna diversity lessens the chance of interference, and increases the signal-to-noise ratio.

Make use of antenna diversity in your MANET network design to optimise it for best performance.