Radio Link Choice: Microwave Radio or IP Radio
Important Considerations for 5GHz Outdoor Radio Links
In the 5GHz band, it is CRITICAL to distinguish between radio link products working in the following bands:
5.47-5.725GHz (ETSI RLAN – Radio Local Area Networks)
5.725-5.850GHz (so-called 5.8GHz ISM Band Radios).
The regulations determining the usage of these bands are VERY different.
5.47-5.725GHz RLAN “IP Radios”
If designing using TDD Outdoor “IP Radios” working between 5.47-5.725GHz, please note that it is mandatory for these links to share the usage of channel with other radios.
The requirement for ‘adaptivity’ specified within EN 301 893 means that shared-access is mandatory. ‘Adaptivity is an automatic channel access mechanism by which a device avoids transmissions in a channel in the presence of transmissions from other RLAN systems in that channel.’ (reference ETSI, 2012)
ETSI. (2012). ETSI EN 301 893 V1.7.1 (2012-06) Broadband Radio Access Networks (BRAN);5 GHz high performance RLAN; Harmonized EN covering the essential requirements of article 3.2 of the R&TTE Directive.
So, latency, variation of latency, throughput speed and variation of throughput speed will vary depending on the number of other radios “sharing” the channel. Furthermore, the number of sharing users can change with time, thereby affecting your link.
Transmit power limitations are another consideration. Consider the example for South Africa:
- 5470-5725MHz (see GAZETTE, 2008 reference below) (channels 100 to 140), 1W (+30dBm) EIRP, Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) are obligatory, EN 301 893, EN 301 489-1,17, EN60950, ITU-R.1625
GAZETTE, G. (2008). 29 JULY 2008, No. 31290. SOUTH AFRICA GOVERNMENT GAZETTE.
NOTE the RLAN EIRP is 1W, whereas for the ISM Band, the EIRP is 200W.
5.725-5.850GHz “5.8GHz” ISM Band Microwave Radios
If one does not have a frequency channel license and one wants low and constant latency (sub-500 microseconds) and constant, guaranteed data throughput speeds, then use Full Duplex Microwave (PDH) radio links that work in the 5.725-5.850GHz ISM band.
Sagittar SGT-LPN58V links are supplied with +20dBm or +27dBm transmit power levels.
Again, let us consider EIRP regulations, this time for the ISM Band, using South Africa as an example:
- 5725-5850MHz (GAZETTE, 2 DECEMBER 2009, No. 32769, 2009), ISM Band: 4W (36dBm) PtMP EIRP, 200W (53dBm) PtP EIRP (digital modulation only and the nominal bandwidths of transmission must not be less than 1MHz)
A key objective is highest possible C/I (Carrier-to-Interference) at the receiver. When given the choice of ISM 200W EIRP vs RLAN 1W EIRP, ISM offers distinct benefits. Higher C/I allows a link to provide higher capacity throughput using higher order modulation.
Given the above, we can summarise as follows:
For Outdoor transmission, there are two bands
- 5.470-5.725 GHz (RLAN Band)
- 5.725-5.850 GHz (ISM Band)
One can describe two interference mechanisms
1) in RLAN, interference forces radios to stop and let other radios transmit (equitable sharing of access to channel bandwidth). Rule in RLAN: radios must obey EN 301 893 i.e. adapt and share access to the bandwidth resource.
2) in ISM: interference can make a radio change modulation from 64QAM down to BPSK, thereby avoiding the effects of interference. Rule in ISM: radios must accept interference of other radios i.e. the radio tries its best to transmit data in the face of interference.
The choice of technologies, whether Microwave Radio or IP Radios and the use of different topology options each has their place depending on amongst other:
- User Requirements
- Application: Voice-only vs Voice/Data vs Voice/Video/Data
- Voice-quality objectives (affected by the possibility of link errors and latency)
- Data throughput capacity (if the intention is to share application functions for the links – i.e., rather than voice-only, a sharing of voice, video and data functionality).
- Constant or variable data throughput speeds (for links or the network)
- Constant or variable latency (for links or the network)
- Protection-requirements to ensure 99.99x% link or network availability
- Types of interfaces to be used (Ethernet, E1, STM)
- Availability (or lack) of frequency assets (frequencies and bandwidth)
- Link Distance – multipath increases with link distance: either diversity or high fade margin designs are used to help reduce link outage probability
- Climate where network will be installed (determines choice of preferred frequency bands)
- Budget and timescales (‘project management’ and ‘long-term planning’ are mandatory for microwave radio link projects – even the cost to ship 0.6m high performance antennas by air freight can exceed the cost of the antenna). Sea freight is normally used to send high-performance antennas, hence the mandatory requirement for long-term planning when project budget-constraints are of critical importance.
- Building, tower or mast considerations:
- Heights (are the structures high enough to allow placement of antennas at the heights required by the radio link design process?)
- Is there spare/additional-space on the structure for placement of new antennas
- Mechanical loading constraints – too much extra loading by new antennas could possibly lead to unacceptable swaying and twisting of the antenna mounting structure.
- Space (or lack thereof) in equipment rooms
- Coverage area and size of the network (e.g. in order to complete a ring)
- Power supply types may affect the choice of equipment
Sagittar Microwave Radio Links – Africa, Middle East and SE Asia
Sagittar Microwave Radio Link Solutions
Email us at [email protected]
Or, please follow this link to ask questions and request additional information.