This analysis has highlighted some key considerations for microwave network design.

The results obtained by means of increased HQAM levels can be considered as a network average. As noted, 128QAM represents the modulation index beyond which there is a strong applicability decline. This is an issue in network aggregation, where a network upgrade or redesign can have significant impact. Even in the tail parts of a network, application of 1024QAM and higher-order modulation formats must be carefully considered, unless service availability is not the primary concern (such as a move from 99.995% availability to 99.99%).

In reality, it may make little sense to scale aggregation links already operating at 64QAM to 128QAM to higher-order modulation formats, since those links are generally designed to operate at 99.999% because of their functionality of grooming traffic in the middle of the network. The main potential to improve modulation rests with the tail portions of the wireless networks, where HQAM can be exploited.

If an increase in the modulation index is the primary means scaling capacity, that choice provides a certain level of uncertainty: for example, given a certain link, there is not full confidence to reach the desired capacity level because of the network status. An alternative solution to HQAM, with a higher degree of confidence in terms of feasibility deployment, is Cross-Polar Interference Cancelation (XPIC): This option has not been considered in the current analysis but provides a 2X increase with larger applicability in a network, at the cost of new equipment. Given the characteristics of the network analyzed, packet compression provides “only” a 1.4X gain, but with the significant advantage that it can be applied everywhere without any changes to the physical network.

The question that might arise at this point is “which is the best technology?” Unless network specifics constrain an operator to prefer one mechanism, the best solution might employ a mix of technologies to achieve different requirements of network domains and services. For example, in network aggregation where interference might be a serious issue, the combined use of XPIC and packet compression provides a nominal gain close to 2X x 1.4X, a factor 3X from the pure application of HQAM and ready to support the launch of LTE services.5

In summary, two independent technologies have been examined which can be applied at the same time to scale microwave link and/or network capacity. Modern microwave networks will increasingly require the joint application of even more microwave optimization technologies to sustain the backhaul demands of the new generations of RAN technologies such as LTE, small cells, and LTE-Advanced (LTE-A) wireless communications. Packet-based scaling technologies will play an increasingly important role in microwave transmission: They support scaling capacity in existing RF/microwave networks without impacting microwave CAPEX and/or OPEX. These technologies will be further detailed in subsequent articles. One of these articles will examine packet compression algorithms, while another will review multichannel technologies and efforts to reach a capacity threshold thought as unconceivable only a few years back: 10 Gbit/s over the air.

Acknowledgments

The author wishes to greatly thank his colleagues Roberto Valtolina and Mario Frecassetti, both Product Managers of the Microwave Business Unit of Alcatel-Lucent, and Scott Larrigan of Product Marketing, for their precious support.

References

1. “Test Methodology Journal: IMIX (Internet Mix) Journal.”

2. “Packet Microwave: Boosting Capacity For Long-Term Growth.”  

3. ITU-R  SM.1046-2, “Definition of spectrum use and efficiency of a radio system,” May 2006.

4. ETSI ATTMTM4(12)000056, “Energy efficiency models,”Alcatel-Lucent contribution to TR 103 820 “Energy efficiency metrics and test procedures for point-to-point fixed radio systems.”

5. L. Steenkamp, “Mobile capacity solution,” France Telecom/Orange presentation at Packet Microwave Forum, October 2012.