Wireless Data Technologies MM Clements

WDT 2 Last Week Noise in wireless systems SNR – measured in dBs Some noise can be filtered out Some can be avoided after a site survey Some noise can be avoided by careful choice of hardware Some noise cannot ever be removed

WDT 3 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

WDT 4 WiMAX IEEE Promises to deliver high data rates cheaply to remote regions Operates in two separate frequency bands, 2-11 GHz and 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

WDT 5 Where WiMAX fits into Networking MAN solution Bridges gap to WAN Solves last mile Still not fully deployed in UK Suits rural areas

WDT 6 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 x to bridge the distance between the x wireless access point and a core network WiMAX may also replace x in certain network topologies

WDT 7 1 st Generation IEEE d 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

WDT 8 2 nd Generation IEEE d 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

WDT 9 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

WDT 10 3 rd Generation IEEE e 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

WDT 11 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

WDT 12 LOS Bandwidth Predictions are 280 Mbps supplied to Access point in a neighbourhood This will be distributed out to domestic customers

WDT 13 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

WDT 14 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

WDT 15 Multipath Interference

WDT 16 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

WDT 17 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.

WDT 18 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.

WDT 19 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

WDT 20 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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WDT 22 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.

WDT 23 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.

WDT 24 Convergence of Technologies In the short-term future, the x 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 x 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, x and Cellular-enabled, however only time will tell as to which the winning technology combination is likely to be.

WDT 25 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 x for some time Customers may get up to 15 Mbps from access points