The data storm kicked up by the rise in data use from smartphones and tablet computers necessitates a focus on scaling microwave capacity efficiently.
Microwave networks can be adjusted for spectral efficiency on a link-by-link basis, but this is not practical. What’s needed is a network-based approach such as that used in the Alcatel-Lucent 9500 Microwave Packet Radio that can avoid optimizations that are only valid on a small scale, and reduce the amount of spectrum used to help save rights-of-use costs.
According to a recent Alcatel-Lucent TechZine article, operators have two good microwave scaling methods at their disposal on the topic, hierarchical quadrature amplitude modulation (HQAM) and packet compression.
HQAM leverages higher-order modulation to maximize spectral efficiency over a microwave communications channel. For example, the 512-state quadrature amplitude modulation (512QAM) and 1024QAM formats provide a combined sequential gain of about 25 percent in useable traffic capacity compared to 256QAM, according to Alcatel-Lucent.
Packet compression can also reduce overhead introduced by a frame or packet structure to help increase in spectral efficiency in a full packet-based environment. Packet compression works on the protocol overhead portions of IP packets, according to the blog post. Fields belonging to Ethernet, Multiprotocol Label Switching (MPLS), IP, and TCP/UDP and are compressed before transmission and rebuilt at the receiving end of a microwave link. Gains from compression can be as high as 40 percent with IPv4, and almost double that when IPv6 is used.
To gauge how these two techniques can benefit operators in practice, Alcatel-Lucent analyzed an operational European mobile backhaul network with 890 short-haul links.
It found that the best potential to improve modulation is found in the tail portions of wireless networks where HQAM can be exploited, or in long-haul microwave transmission where there is less potential for interference, according to the blog.
“In short-haul transmissions, HQAM becomes much less applicable beyond a modulation index of 128QAM,” the blog noted. “Even in tail parts of a network, using 1024QAM and higher-order modulation formats must be carefully considered, unless service availability is not the primary concern.”
It also found that there is some uncertainty when increasing the modulation index is the primary means of scaling capacity in short-haul applications, and unless network specifics constrain an operator to 1 mechanism, the best solution might be to mix technologies to achieve the best results.
“HQAM and packet compression are independent technologies that can be applied at the same time to scale microwave link and network capacity,” the blog noted. “Looking ahead, packet-based scaling technologies will play an increasingly important role in microwave transmission.”
