Wireless Data Technologies

MM Clements

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Last Week

Noise in wireless systemsSNR – measured in dBsSome noise can be filtered outSome can be avoided after a site

surveySome noise can be avoided by careful

choice of hardwareSome noise cannot ever be removed

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This week……….

Worldwide Interoperability for Microwave Access WiMAX as a solution What it promises to deliver LOS vs. NLOS operation Mobile vs. static installations Multipath interference mitigation Regulations

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WiMAX IEEE 802.16

Promises to deliver high data rates cheaply to remote regions

Operates in two separate frequency bands, 2-11 GHz and 10-66 GHz

At the higher frequencies, line of sight (LOS) is required – point-to-point links only

In the lower region, the signals propagate without the requirement for line of sight (NLOS) to customers

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Where WiMAX fits into Networking

MAN solutionBridges gap to

WANSolves last mileStill not fully

deployed in UKSuits rural areas

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WiMAX and its positioning

WiMAX LOS is envisaged to provide the high data rate backhaul to a core network

WiMAX is a complimentary technology to 802.11x to bridge the distance between the 802.11x wireless access point and a core network

WiMAX may also replace 802.11x in certain network topologies

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1st Generation IEEE 802.16d

Fixed solutions only Offers high data rate Operates in 2 – 11 GHz range Provider chooses frequency of use Can transmit up to 30 miles (50km) ISP may use this in remote areas Cheaper than laying in wired infrastructure

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2nd Generation IEEE 802.16d

These devices will are indoor devices similar to cable or DSL modems and

WiMAX and WiFi enabled No truck roll required Customer can set this up indoors Plug n play

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What is a Truck Roll?

Required for non-customer installable equipment

Technician needs to install hardware

Costs much and may take 1 year subscription to recoup

Industry prefers plug n play

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3rd Generation IEEE 802.16e

These devices will be for laptops and other portable devices

Not legal in UK at present - OFCOM 2-11 GHz non-directional wireless signals May be embedded into mobile handsets Convergence may be around the corner

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LOS vs NLOS

•Higher frequencies for WiMAX are line of sight•Used as a backhaul to Internet or corporate network•These are point-to-point•Run between a company's infrastructure nodes •Alternatively between a service provider and a customer who requires very high BW to distribute themselves

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LOS Bandwidth

Predictions are 280 Mbps supplied to Access point in a neighbourhood

This will be distributed out to domestic customers

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NLOS for the End User

Plug n play end users will be using NLOS WiMAX

Traditionally there has been a problem propagating wireless in urban areas

Buildings cause signal reflections Degrades signal badly

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Multipath Interference

Sometimes called picket fencing or flutter Happens when wireless signals bounce around

between obstructions that lie between the transmitter and receiver

Direct path between the transmitter and receiver and a secondary path exist

Secondary path is longer path and therefore a percentage of the power of the original signal arrives later than the signal that travelled via the direct path

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Multipath Interference

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Timing Problem in NLOS

As some signals have further to travel, part of signal may be delayed by a microsecond or so

Can be spotted on analogue TV when a second ghost image appears on screen shifted to the right of the strong signal

Causes problems with digital transmissions WiMAX has a solution to this for its end

customers

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NLOS Base Stations

Smart device that uses DSP to control an array of radiating elements

Each element fed same signal, but differs in its amplitude and phase and time delay

Transmitted signals are calculated to arrive at destination at the same time, having taken into account the various different paths that the signals will undergo on their journey to the receiver.

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Example

Base station may receive a signal from the west and then 1 microsecond later the same signal, 6dB weaker from the south.

DSP hardware in base station transmits a signal in 2 parts

It transmits a strong signal to the south and a microsecond later a 6dB weaker signal to the west

This overcomes the physical limitations of the area and the arriving signal at the customer premises arrives all at once and in phase, producing an amplified signal.

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Monitoring Signals at Base Station

To operate, base station monitors all received signals

Customers equipment transmits and base station checks for multipath interference

DSP used to prepare its transmission characteristics

Must be done frequently as moving objects cause interference too

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NLOS vs. Mesh

Meshed networks need many TX/ RX ISP cannot afford this every 50 metres or so Solution is to allow customer equipment to

form the mesh Trialled in USA currently by Nokia Neighbourhood is divided into a number of

AirHoods each of which is served by an Airhead

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Drawback Of Any Meshed Solution

Mesh means that more hops will be experienced by data latency

Shortness of hops will keep signal power and hence data rates high - advantage

Real-time applications will suffer in a mesh network of this type

QoS software upgrades to participating end-user nodes can address real-time latency issues with smart queuing techniques.

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Spectrum Licensing and Usage

Unfortunately, the licensing of the 2.4 GHz band in Europe only allows for a transmission power of 100 mW as compared to the USA who have licensed the maximum power of the same band at 4W.

Unless and until the maximum power allowable on this band changes upwards, it is unlikely that the meshed solution will be seen in Europe.

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Convergence of Technologies

In the short-term future, the 802.11x hotspot market will grow and will be serviced by p-to-p LOS WiMAX for the backhaul

The WiMAX market will grow over time and wireless access points will eventually support WiMAX and 802.11x

It is also highly likely that VoIP will penetrate all of the communication market and that cellular telephony will also be WiMAX enabled

It is easy to envisage access points that will be WiMAX, 802.11x and Cellular-enabled, however only time will tell as to which the winning technology combination is likely to be.

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Conclusion

WiMAX has LOS and NLOS Backhaul will be p-to-p and LOS NLOS suffers from flutter but can be solved

with smart base stations WiMAX may replace last mile to subscribers May not eclipse 802.11x for some time Customers may get up to 15 Mbps from access

points