Implementing Microwave for High Speed Internet ISP Backbones in the Middle East
CableFree FOR3 Microwave links are being installed by ISPs in Iraq for Internet Backbone Connectivity. These links offer 880Mbps full duplex capacity with easy upgrade capability to 2+0 for 1.76Gbps full duplex, and are typically installed on towers or buildings for clear Line of Sight between network node locations.
High Capacity Microwave
CableFree FOR3 can expand to 3.5Gbps and above for ultra high capacity links. Microwave links are fast to install and can be deployed within hours, and distances up to 100km or more on suitable towers.
Microwave is low cost alternative to fibre optic and leased line connectivity and are highly reliable with uptimes of 99.999% or higher possible.
Pictures from Iraq from CableFree regional partner Noor AKD.
CableFree Products are used extensively in the Middle East region with installations in countries including Iraq, UAE, Saudi Arabia, Kuwait, Egypt, Lebanon, Turkey and several others
Rain fade refers primarily to the absorption of a microwave radio frequency (RF) signal by atmospheric rain, snow or ice, and losses which are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a storm front. Rain fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the satellite dish has a low look angle. From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow or ice on the uplink or downlink antenna reflector, radome or feed horn. Rain fade is not limited to satellite uplinks or downlinks, it also can affect terrestrial point to point microwave links (those on the earth’s surface).
Possible ways to overcome the effects of rain fade are site diversity, uplink power control, variable rate encoding, receiving antennas larger (i.e. higher gain) than the required size for normal weather conditions, and hydrophobic coatings.
Two models are generally used for Rain modelling: Crane and ITU. The ITU model is generally preferred by microwave planners. A global map of Rain distribution according to the ITU model is shown below:
Used in conjunction with appropriate planning tools, this data can be used to predict the expected Operational Availability (in %) of a microwave link. Useful Operational Availability figures typically vary from 99.9% (“three nines”) to 99.999% (“five nines”), and are a function of the overall link budget including frequency band, antenna sizes, modulation, receiver sensitivity and other factors.
Another useful Rain Fade map is shown here, showing the 0.01% annual rainfall exceedance rate:
For more information on this topic, please contact us
In radio technology, multiple-input and multiple-output, or MIMO , is a method for multiplying the capacity of a radio link using multiple transmit and receive antennas to exploit multipath propagation.
Earlier usage of the term “MIMO” referred to the use of multiple antennas at both the transmitter and the receiver. In modern usage, “MIMO” specifically refers to a practical technique for sending and receiving more than one data signal on the same radio channel at the same time via multipath propagation. MIMO is fundamentally different from smart antenna techniques developed to enhance the performance of a single data signal, such as beamforming and diversity.
MIMO can be sub-divided into three main categories, precoding, spatial multiplexing or SM, and diversity coding.
Precoding is multi-stream beamforming, in the narrowest definition. In more general terms, it is considered to be all spatial processing that occurs at the transmitter. In (single-stream) beamforming, the same signal is emitted from each of the transmit antennas with appropriate phase and gain weighting such that the signal power is maximized at the receiver input. The benefits of beamforming are to increase the received signal gain – by making signals emitted from different antennas add up constructively – and to reduce the multipath fading effect. In line-of-sight propagation, beamforming results in a well-defined directional pattern. However, conventional beams are not a good analogy in cellular networks, which are mainly characterized by multipath propagation. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas, and precoding with multiple streams is often beneficial. Note that precoding requires knowledge of channel state information (CSI) at the transmitter and the receiver.
Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high-rate signal is split into multiple lower-rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser of the number of antennas at the transmitter or receiver. Spatial multiplexing can be used without CSI at the transmitter, but can be combined with precoding if CSI is available. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access or multi-user MIMO, in which case CSI is required at the transmitter. The scheduling of receivers with different spatial signatures allows good separability.
Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding. Diversity coding can be combined with spatial multiplexing when some channel knowledge is available at the transmitter.
Forms of MIMO
Multi-antenna MIMO (or Single user MIMO) technology has been developed and implemented in some standards, e.g., 802.11n products.
Per Antenna Rate Control (PARC), Varanasi, Guess (1998), Chung, Huang, Lozano (2001)
Selective Per Antenna Rate Control (SPARC), Ericsson (2004)
The physical antenna spacing is selected to be large; multiple wavelengths at the base station. The antenna separation at the receiver is heavily space-constrained in handsets, though advanced antenna design and algorithm techniques are under discussion.
XPIC is a feature used on Carrier-Class Microwave Link installations to increase capacity and spectral efficiency of a link.
A Microwave Link using XPIC technology capabilities effectively doubles the potential capacity of a Microwave Path.
XPIC allows the assignment of the same frequency to both the vertical & horizontal Polarization on a Path. Where available frequencies are limited then it is possible to assign the same frequency twice on the same path using both Polarizations.
Using standard Microwave equipment from any of the major manufacturers, if a full block of eight frequencies were available for a 6 GHz Lower band path then eight frequencies could be assigned in each direction on the path, four per polarization.
By comparison. using equipment with XPIC capability, sixteen frequencies may be assigned each way on the same path (eight per polarization).