by Stuart Little, Harris Stratex; Trevor Manning, TMC Global Ltd.
Operators are faced with the challenge of providing enough transmission capacity for the almost exponential demand in bandwidth from new data services, while constrained by a relatively modest increase in revenue from those services (see Figure 1). This additional bandwidth demand is not an issue for fiber optic transmission systems, which have virtually limitless capacity. However, radio systems are constrained in capacity by available radio frequency (RF) bandwidth and can suffer quality degradations during atmospheric irregularities.
Conversely, fiber is not readily available in the access portion of the network and is too time consuming and costly to provide in a ubiquitous manner. Therefore, microwave radio will continue to be the technology of choice for next-generation access networks, compelling a solution to the problem of constrained bandwidth.
Figure 1 The end of the 'Voice Era' and the increase in demand for data traffic is creating a widening 'Revenue Gap'.
User data throughput can be increased in a fixed RF bandwidth through the use of more complex modulation schemes, improving the bits/Hz efficiency. However, historically, this came at the cost of all the traffic being more susceptible to noise and interference. Thus, there was a trade-off between quality and capacity. This was a one-off decision that had to be made at the design phase, where the choice was either to deploy radios with a low modulation scheme, which could achieve higher availability and performance for a given size of antenna, or have much higher capacity in the same RF bandwidth, but with a lower level of quality for all traffic. Alternatively, to achieve the same Quality of Service (QoS) metrics, extra expense had to be incurred by deploying larger antennas on the radio hops.
ACM Unlocks Additional Capacity
Microwave radio systems have now evolved that can provide significantly more capacity in a fixed RF bandwidth—at the equivalent level of service to fiber. The key technology enabler for this is Adaptive Coding and Modulation (ACM).
Interested in reading the complete article?
A complete view is available to registered MWJournal.com members.
Registration is FREE! Click here to register.
Already registered? Login >>
Already a member, but don't remember your username and/or password? Click here.
If you are a Microwave Journal monthly subscriber and would like to enable FREE Website access, please click here.
